{
  "title": "Substitution Method - Grade 10 CBSE",
  "total_questions": 100,
  "questions": [
    {"id": 1, "difficulty": "easy", "question": "Solve using substitution: x + y = 5, x - y = 1", "options": {"A": "x=2, y=3", "B": "x=3, y=2", "C": "x=4, y=1", "D": "x=1, y=4"}, "correct_answer": "B"},
    {"id": 2, "difficulty": "easy", "question": "Solve using substitution: 2x + y = 7, x = 2", "options": {"A": "x=2, y=2", "B": "x=2, y=3", "C": "x=2, y=5", "D": "x=2, y=4"}, "correct_answer": "B"},
    {"id": 3, "difficulty": "easy", "question": "Solve: x = 3y, x + y = 12", "options": {"A": "x=6, y=2", "B": "x=9, y=3", "C": "x=8, y=4", "D": "x=10, y=2"}, "correct_answer": "B"},
    {"id": 4, "difficulty": "easy", "question": "Solve: y = 2x - 1, x + y = 8", "options": {"A": "x=2, y=6", "B": "x=3, y=5", "C": "x=4, y=4", "D": "x=5, y=3"}, "correct_answer": "B"},
    {"id": 5, "difficulty": "easy", "question": "Solve: x = y + 2, 2x + y = 10", "options": {"A": "x=4, y=2", "B": "x=3, y=1", "C": "x=5, y=3", "D": "x=6, y=4"}, "correct_answer": "A"},
    {"id": 6, "difficulty": "easy", "question": "Solve: 3x + y = 10, y = 4", "options": {"A": "x=1, y=4", "B": "x=2, y=4", "C": "x=3, y=4", "D": "x=4, y=4"}, "correct_answer": "B"},
    {"id": 7, "difficulty": "easy", "question": "Solve: x + 2y = 7, x = 1", "options": {"A": "x=1, y=2", "B": "x=1, y=3", "C": "x=1, y=4", "D": "x=1, y=5"}, "correct_answer": "B"},
    {"id": 8, "difficulty": "easy", "question": "Solve: y = x - 2, 2x + y = 7", "options": {"A": "x=3, y=1", "B": "x=4, y=2", "C": "x=5, y=3", "D": "x=6, y=4"}, "correct_answer": "A"},
    {"id": 9, "difficulty": "easy", "question": "Solve: x = 2y, 3x - y = 10", "options": {"A": "x=4, y=2", "B": "x=6, y=3", "C": "x=8, y=4", "D": "x=10, y=5"}, "correct_answer": "A"},
    {"id": 10, "difficulty": "easy", "question": "Solve: 2x - y = 3, y = 5", "options": {"A": "x=3, y=5", "B": "x=4, y=5", "C": "x=5, y=5", "D": "x=6, y=5"}, "correct_answer": "B"},
    {"id": 11, "difficulty": "easy", "question": "Solve: x + y = 9, x = y + 1", "options": {"A": "x=4, y=5", "B": "x=5, y=4", "C": "x=6, y=3", "D": "x=7, y=2"}, "correct_answer": "B"},
    {"id": 12, "difficulty": "easy", "question": "Solve: 3y = x, x + y = 8", "options": {"A": "x=4, y=4", "B": "x=5, y=3", "C": "x=6, y=2", "D": "x=7, y=1"}, "correct_answer": "C"},
    {"id": 13, "difficulty": "easy", "question": "Solve: y = 3x - 2, x + y = 10", "options": {"A": "x=2, y=8", "B": "x=3, y=7", "C": "x=4, y=6", "D": "x=5, y=5"}, "correct_answer": "B"},
    {"id": 14, "difficulty": "easy", "question": "Solve: x = 4, 2x + y = 11", "options": {"A": "x=4, y=2", "B": "x=4, y=3", "C": "x=4, y=4", "D": "x=4, y=5"}, "correct_answer": "B"},
    {"id": 15, "difficulty": "easy", "question": "Solve: x - y = 2, x = 7", "options": {"A": "x=7, y=4", "B": "x=7, y=5", "C": "x=7, y=6", "D": "x=7, y=7"}, "correct_answer": "B"},
    {"id": 16, "difficulty": "easy", "question": "Solve: y = 2x + 1, 3x + y = 11", "options": {"A": "x=1, y=3", "B": "x=2, y=5", "C": "x=3, y=7", "D": "x=4, y=9"}, "correct_answer": "B"},
    {"id": 17, "difficulty": "easy", "question": "Solve: x + 3y = 10, x = 4", "options": {"A": "x=4, y=1", "B": "x=4, y=2", "C": "x=4, y=3", "D": "x=4, y=4"}, "correct_answer": "B"},
    {"id": 18, "difficulty": "easy", "question": "Solve: 2x = y + 3, x + y = 9", "options": {"A": "x=3, y=6", "B": "x=4, y=5", "C": "x=5, y=4", "D": "x=6, y=3"}, "correct_answer": "B"},
    {"id": 19, "difficulty": "easy", "question": "Solve: y = 5, x + 2y = 13", "options": {"A": "x=1, y=5", "B": "x=2, y=5", "C": "x=3, y=5", "D": "x=4, y=5"}, "correct_answer": "C"},
    {"id": 20, "difficulty": "easy", "question": "Solve: x = y - 1, 2x + y = 8", "options": {"A": "x=2, y=3", "B": "x=3, y=4", "C": "x=4, y=5", "D": "x=5, y=6"}, "correct_answer": "A"},
    {"id": 21, "difficulty": "medium", "question": "Solve using substitution: 2x + 3y = 7, 4x - y = 3", "options": {"A": "x=1, y=2", "B": "x=2, y=1", "C": "x=1, y=1", "D": "x=2, y=2"}, "correct_answer": "C"},
    {"id": 22, "difficulty": "medium", "question": "Solve using substitution: 3x + 2y = 8, 2x - y = 3", "options": {"A": "x=2, y=1", "B": "x=1, y=2", "C": "x=3, y=0", "D": "x=0, y=3"}, "correct_answer": "A"},
    {"id": 23, "difficulty": "medium", "question": "Solve using substitution: 5x + 2y = 11, 3x - y = 4", "options": {"A": "x=1, y=3", "B": "x=2, y=1", "C": "x=3, y=-2", "D": "x=4, y=-1"}, "correct_answer": "B"},
    {"id": 24, "difficulty": "medium", "question": "Solve using substitution: x + 4y = 9, 2x - 3y = 4", "options": {"A": "x=1, y=2", "B": "x=2, y=1", "C": "x=3, y=1", "D": "x=4, y=1"}, "correct_answer": "C"},
    {"id": 25, "difficulty": "medium", "question": "Solve using substitution: 3x - 2y = 7, x + y = 4", "options": {"A": "x=3, y=1", "B": "x=2, y=2", "C": "x=4, y=0", "D": "x=5, y=-1"}, "correct_answer": "A"},
    {"id": 26, "difficulty": "medium", "question": "Solve using substitution: 2x + 5y = 12, 3x - y = 1", "options": {"A": "x=1, y=2", "B": "x=2, y=1", "C": "x=3, y=0", "D": "x=4, y=-1"}, "correct_answer": "A"},
    {"id": 27, "difficulty": "medium", "question": "Solve using substitution: 4x + 3y = 10, 2x - y = 0", "options": {"A": "x=1, y=2", "B": "x=2, y=4", "C": "x=3, y=6", "D": "x=4, y=8"}, "correct_answer": "A"},
    {"id": 28, "difficulty": "medium", "question": "Solve using substitution: x + 2y = 5, 3x - 4y = 2", "options": {"A": "x=2, y=1.5", "B": "x=3, y=1", "C": "x=4, y=0.5", "D": "x=5, y=0"}, "correct_answer": "A"},
    {"id": 29, "difficulty": "medium", "question": "Solve using substitution: 2x - 3y = 1, x + 2y = 8", "options": {"A": "x=4, y=2", "B": "x=5, y=1.5", "C": "x=6, y=1", "D": "x=7, y=0.5"}, "correct_answer": "B"},
    {"id": 30, "difficulty": "medium", "question": "Solve using substitution: 5x - 2y = 8, 3x + y = 7", "options": {"A": "x=1, y=4", "B": "x=2, y=1", "C": "x=3, y=-2", "D": "x=4, y=-5"}, "correct_answer": "B"},
    {"id": 31, "difficulty": "medium", "question": "Solve using substitution: 3x + 4y = 10, 2x - y = 1", "options": {"A": "x=1, y=2", "B": "x=2, y=1", "C": "x=3, y=0.25", "D": "x=4, y=-0.5"}, "correct_answer": "B"},
    {"id": 32, "difficulty": "medium", "question": "Solve using substitution: x + 3y = 7, 2x - y = 4", "options": {"A": "x=1, y=2", "B": "x=2, y=1", "C": "x=3, y=0", "D": "x=4, y=-1"}, "correct_answer": "A"},
    {"id": 33, "difficulty": "medium", "question": "Solve using substitution: 4x - y = 6, 3x + 2y = 7", "options": {"A": "x=1, y=-2", "B": "x=2, y=2", "C": "x=3, y=6", "D": "x=4, y=10"}, "correct_answer": "B"},
    {"id": 34, "difficulty": "medium", "question": "Solve using substitution: 2x + y = 5, 3x - 2y = 4", "options": {"A": "x=1, y=3", "B": "x=2, y=1", "C": "x=3, y=-1", "D": "x=4, y=-3"}, "correct_answer": "B"},
    {"id": 35, "difficulty": "medium", "question": "Solve using substitution: x - 2y = 3, 3x + y = 11", "options": {"A": "x=1, y=2", "B": "x=2, y=3", "C": "x=3, y=0", "D": "x=4, y=0.5"}, "correct_answer": "C"},
    {"id": 36, "difficulty": "medium", "question": "Solve using substitution: 5x + 3y = 16, 2x - y = 1", "options": {"A": "x=1, y=3", "B": "x=2, y=2", "C": "x=3, y=1", "D": "x=4, y=0"}, "correct_answer": "B"},
    {"id": 37, "difficulty": "medium", "question": "Solve using substitution: 3x - 4y = 2, x + y = 3", "options": {"A": "x=1, y=2", "B": "x=2, y=1", "C": "x=3, y=0", "D": "x=4, y=-1"}, "correct_answer": "B"},
    {"id": 38, "difficulty": "medium", "question": "Solve using substitution: 2x + 3y = 13, x - y = 1", "options": {"A": "x=2, y=3", "B": "x=3, y=2", "C": "x=4, y=3", "D": "x=5, y=4"}, "correct_answer": "A"},
    {"id": 39, "difficulty": "medium", "question": "Solve using substitution: 4x + y = 9, 3x - 2y = 4", "options": {"A": "x=1, y=5", "B": "x=2, y=1", "C": "x=3, y=-3", "D": "x=4, y=-7"}, "correct_answer": "B"},
    {"id": 40, "difficulty": "medium", "question": "Solve using substitution: x + 5y = 11, 2x - y = 5", "options": {"A": "x=1, y=2", "B": "x=2, y=1", "C": "x=3, y=0", "D": "x=4, y=-1"}, "correct_answer": "A"},
    {"id": 41, "difficulty": "medium", "question": "Solve using substitution: 3x + 2y = 12, 2x - 3y = 5", "options": {"A": "x=2, y=3", "B": "x=3, y=1.5", "C": "x=4, y=0", "D": "x=5, y=-1.5"}, "correct_answer": "B"},
    {"id": 42, "difficulty": "medium", "question": "Solve using substitution: 5x - 3y = 1, 2x + y = 7", "options": {"A": "x=1, y=5", "B": "x=2, y=3", "C": "x=3, y=1", "D": "x=4, y=-1"}, "correct_answer": "B"},
    {"id": 43, "difficulty": "medium", "question": "Solve using substitution: x + 2y = 8, 3x - 4y = 4", "options": {"A": "x=2, y=3", "B": "x=3, y=2.5", "C": "x=4, y=2", "D": "x=5, y=1.5"}, "correct_answer": "C"},
    {"id": 44, "difficulty": "medium", "question": "Solve using substitution: 2x - y = 3, 4x + 3y = 11", "options": {"A": "x=1, y=-1", "B": "x=2, y=1", "C": "x=3, y=3", "D": "x=4, y=5"}, "correct_answer": "B"},
    {"id": 45, "difficulty": "medium", "question": "Solve using substitution: 3x + 4y = 14, x - y = 1", "options": {"A": "x=1, y=0", "B": "x=2, y=1", "C": "x=3, y=2", "D": "x=4, y=3"}, "correct_answer": "B"},
    {"id": 46, "difficulty": "medium", "question": "Solve using substitution: x + 3y = 10, 2x - y = 5", "options": {"A": "x=1, y=3", "B": "x=2, y=2", "C": "x=3, y=1", "D": "x=4, y=0"}, "correct_answer": "C"},
    {"id": 47, "difficulty": "medium", "question": "Solve using substitution: 4x - 3y = 5, 2x + y = 7", "options": {"A": "x=1, y=5", "B": "x=2, y=3", "C": "x=3, y=1", "D": "x=4, y=-1"}, "correct_answer": "B"},
    {"id": 48, "difficulty": "medium", "question": "Solve using substitution: 5x + 2y = 17, 3x - y = 4", "options": {"A": "x=1, y=6", "B": "x=2, y=3.5", "C": "x=3, y=1", "D": "x=4, y=-1.5"}, "correct_answer": "B"},
    {"id": 49, "difficulty": "medium", "question": "Solve using substitution: 2x + 5y = 16, x - 2y = 1", "options": {"A": "x=1, y=2.8", "B": "x=2, y=2.4", "C": "x=3, y=2", "D": "x=4, y=1.6"}, "correct_answer": "C"},
    {"id": 50, "difficulty": "medium", "question": "Solve using substitution: 3x - 2y = 8, x + 3y = 11", "options": {"A": "x=1, y=3.33", "B": "x=2, y=3", "C": "x=3, y=2.67", "D": "x=4, y=2.33"}, "correct_answer": "B"},
    {"id": 51, "difficulty": "medium", "question": "Solve using substitution: x + 4y = 13, 2x - y = 5", "options": {"A": "x=1, y=3", "B": "x=2, y=2.75", "C": "x=3, y=2.5", "D": "x=4, y=2.25"}, "correct_answer": "C"},
    {"id": 52, "difficulty": "medium", "question": "Solve using substitution: 4x + 3y = 19, 3x - 2y = 4", "options": {"A": "x=1, y=5", "B": "x=2, y=3.67", "C": "x=3, y=2.33", "D": "x=4, y=1"}, "correct_answer": "B"},
    {"id": 53, "difficulty": "medium", "question": "Solve using substitution: 2x - 5y = 1, 3x + y = 10", "options": {"A": "x=1, y=7", "B": "x=2, y=4", "C": "x=3, y=1", "D": "x=4, y=-2"}, "correct_answer": "C"},
    {"id": 54, "difficulty": "medium", "question": "Solve using substitution: 5x + 3y = 21, 2x - 4y = 2", "options": {"A": "x=1, y=5.33", "B": "x=2, y=3.67", "C": "x=3, y=2", "D": "x=4, y=0.33"}, "correct_answer": "C"},
    {"id": 55, "difficulty": "medium", "question": "Solve using substitution: x + 2y = 7, 4x - 3y = 3", "options": {"A": "x=1, y=3", "B": "x=2, y=2.5", "C": "x=3, y=2", "D": "x=4, y=1.5"}, "correct_answer": "C"},
    {"id": 56, "difficulty": "medium", "question": "Solve using substitution: 3x - 4y = 7, 2x + y = 8", "options": {"A": "x=1, y=6", "B": "x=2, y=4", "C": "x=3, y=2", "D": "x=4, y=0"}, "correct_answer": "C"},
    {"id": 57, "difficulty": "medium", "question": "Solve using substitution: 2x + 3y = 15, x - y = 2", "options": {"A": "x=1, y=-1", "B": "x=2, y=0", "C": "x=3, y=1", "D": "x=4, y=2"}, "correct_answer": "D"},
    {"id": 58, "difficulty": "medium", "question": "Solve using substitution: 4x + y = 13, 3x - 2y = 4", "options": {"A": "x=1, y=9", "B": "x=2, y=5", "C": "x=3, y=1", "D": "x=4, y=-3"}, "correct_answer": "C"},
    {"id": 59, "difficulty": "medium", "question": "Solve using substitution: 5x - 2y = 11, 3x + y = 10", "options": {"A": "x=1, y=7", "B": "x=2, y=4", "C": "x=3, y=1", "D": "x=4, y=-2"}, "correct_answer": "C"},
    {"id": 60, "difficulty": "medium", "question": "Solve using substitution: x + 3y = 12, 2x - y = 5", "options": {"A": "x=1, y=3.67", "B": "x=2, y=3.33", "C": "x=3, y=3", "D": "x=4, y=2.67"}, "correct_answer": "C"},
    {"id": 61, "difficulty": "medium", "question": "Solve using substitution: 3x + 2y = 14, 4x - 3y = 2", "options": {"A": "x=1, y=5.5", "B": "x=2, y=4", "C": "x=3, y=2.5", "D": "x=4, y=1"}, "correct_answer": "B"},
    {"id": 62, "difficulty": "medium", "question": "Solve using substitution: 2x - 3y = 5, x + 2y = 8", "options": {"A": "x=1, y=3.5", "B": "x=2, y=3", "C": "x=3, y=2.5", "D": "x=4, y=2"}, "correct_answer": "D"},
    {"id": 63, "difficulty": "medium", "question": "Solve using substitution: 4x + 5y = 23, 3x - y = 5", "options": {"A": "x=1, y=3.8", "B": "x=2, y=3", "C": "x=3, y=2.2", "D": "x=4, y=1.4"}, "correct_answer": "B"},
    {"id": 64, "difficulty": "medium", "question": "Solve using substitution: x - 4y = 3, 2x + 3y = 17", "options": {"A": "x=1, y=-0.5", "B": "x=2, y=-0.25", "C": "x=3, y=0", "D": "x=4, y=0.25"}, "correct_answer": "C"},
    {"id": 65, "difficulty": "medium", "question": "Solve using substitution: 5x + 4y = 22, 2x - y = 3", "options": {"A": "x=1, y=4.25", "B": "x=2, y=3", "C": "x=3, y=1.75", "D": "x=4, y=0.5"}, "correct_answer": "B"},
    {"id": 66, "difficulty": "medium", "question": "Solve using substitution: 3x - 5y = 1, 4x + y = 14", "options": {"A": "x=1, y=10", "B": "x=2, y=6", "C": "x=3, y=2", "D": "x=4, y=-2"}, "correct_answer": "C"},
    {"id": 67, "difficulty": "medium", "question": "Solve using substitution: 2x + 7y = 20, x - 3y = 1", "options": {"A": "x=1, y=2.57", "B": "x=2, y=2.29", "C": "x=3, y=2", "D": "x=4, y=1.71"}, "correct_answer": "C"},
    {"id": 68, "difficulty": "medium", "question": "Solve using substitution: 4x - 2y = 6, 3x + 5y = 23", "options": {"A": "x=1, y=4", "B": "x=2, y=3.4", "C": "x=3, y=2.8", "D": "x=4, y=2.2"}, "correct_answer": "B"},
    {"id": 69, "difficulty": "medium", "question": "Solve using substitution: x + 5y = 16, 3x - 2y = 8", "options": {"A": "x=1, y=3", "B": "x=2, y=2.8", "C": "x=3, y=2.6", "D": "x=4, y=2.4"}, "correct_answer": "A"},
    {"id": 70, "difficulty": "medium", "question": "Solve using substitution: 6x + y = 19, 2x - 3y = 5", "options": {"A": "x=1, y=13", "B": "x=2, y=7", "C": "x=3, y=1", "D": "x=4, y=-5"}, "correct_answer": "C"},
    {"id": 71, "difficulty": "medium", "question": "Solve using substitution: 3x + 4y = 18, 5x - 2y = 8", "options": {"A": "x=1, y=3.75", "B": "x=2, y=3", "C": "x=3, y=2.25", "D": "x=4, y=1.5"}, "correct_answer": "B"},
    {"id": 72, "difficulty": "medium", "question": "Solve using substitution: 2x - 5y = 3, 4x + y = 15", "options": {"A": "x=1, y=11", "B": "x=2, y=7", "C": "x=3, y=3", "D": "x=4, y=-1"}, "correct_answer": "C"},
    {"id": 73, "difficulty": "medium", "question": "Solve using substitution: x + 6y = 19, 2x - 3y = 4", "options": {"A": "x=1, y=3", "B": "x=2, y=2.83", "C": "x=3, y=2.67", "D": "x=4, y=2.5"}, "correct_answer": "A"},
    {"id": 74, "difficulty": "medium", "question": "Solve using substitution: 4x - 3y = 9, 2x + 5y = 17", "options": {"A": "x=1, y=3", "B": "x=2, y=2.6", "C": "x=3, y=2.2", "D": "x=4, y=1.8"}, "correct_answer": "C"},
    {"id": 75, "difficulty": "medium", "question": "Solve using substitution: 5x + 2y = 21, 3x - 4y = 1", "options": {"A": "x=1, y=8", "B": "x=2, y=5.5", "C": "x=3, y=3", "D": "x=4, y=0.5"}, "correct_answer": "C"},
    {"id": 76, "difficulty": "medium", "question": "Solve using substitution: 2x + 3y = 16, 5x - y = 12", "options": {"A": "x=1, y=4.67", "B": "x=2, y=4", "C": "x=3, y=3.33", "D": "x=4, y=2.67"}, "correct_answer": "B"},
    {"id": 77, "difficulty": "medium", "question": "Solve using substitution: x - 2y = 5, 3x + 4y = 17", "options": {"A": "x=1, y=-2", "B": "x=2, y=-1.5", "C": "x=3, y=-1", "D": "x=4, y=-0.5"}, "correct_answer": "C"},
    {"id": 78, "difficulty": "medium", "question": "Solve using substitution: 4x + 3y = 25, 2x - y = 5", "options": {"A": "x=1, y=7", "B": "x=2, y=5.67", "C": "x=3, y=4.33", "D": "x=4, y=3"}, "correct_answer": "D"},
    {"id": 79, "difficulty": "medium", "question": "Solve using substitution: 3x - 2y = 12, x + 3y = 11", "options": {"A": "x=1, y=3.33", "B": "x=2, y=3", "C": "x=3, y=2.67", "D": "x=4, y=2.33"}, "correct_answer": "B"},
    {"id": 80, "difficulty": "medium", "question": "Solve using substitution: 2x + 5y = 23, 3x - 2y = 4", "options": {"A": "x=1, y=4.2", "B": "x=2, y=3.8", "C": "x=3, y=3.4", "D": "x=4, y=3"}, "correct_answer": "D"},
    {"id": 81, "difficulty": "hard", "question": "Solve using substitution: 0.2x + 0.3y = 1.3, 0.4x + 0.5y = 2.3", "options": {"A": "x=1, y=3", "B": "x=2, y=3", "C": "x=3, y=2", "D": "x=4, y=1"}, "correct_answer": "B"},
    {"id": 82, "difficulty": "hard", "question": "Solve using substitution: (x/2) + (y/3) = 2, (x/3) + (y/2) = 13/6", "options": {"A": "x=1, y=3", "B": "x=2, y=3", "C": "x=3, y=2", "D": "x=4, y=1"}, "correct_answer": "B"},
    {"id": 83, "difficulty": "hard", "question": "Solve using substitution: 3/(x+y) + 2/(x-y) = 3, 9/(x+y) - 4/(x-y) = 2", "options": {"A": "x=3, y=2", "B": "x=4, y=1", "C": "x=5, y=0", "D": "x=6, y=-1"}, "correct_answer": "A"},
    {"id": 84, "difficulty": "hard", "question": "Solve using substitution: (3x+2y)/4 = (x+4y)/3 = 5", "options": {"A": "x=4, y=3", "B": "x=6, y=2", "C": "x=8, y=1", "D": "x=10, y=0"}, "correct_answer": "A"},
    {"id": 85, "difficulty": "hard", "question": "Solve using substitution: 2x + 3y = 7, 6x + 9y = 21", "options": {"A": "Infinitely many solutions", "B": "x=1, y=2", "C": "No solution", "D": "x=2, y=1"}, "correct_answer": "A"},
    {"id": 86, "difficulty": "hard", "question": "Solve using substitution: 4x + 6y = 10, 2x + 3y = 6", "options": {"A": "x=1, y=1", "B": "x=2, y=0.33", "C": "No solution", "D": "Infinitely many solutions"}, "correct_answer": "C"},
    {"id": 87, "difficulty": "hard", "question": "Solve using substitution: 0.5x + 0.2y = 2.4, 0.25x + 0.1y = 1.2", "options": {"A": "x=2, y=7", "B": "x=4, y=2", "C": "Infinitely many solutions", "D": "No solution"}, "correct_answer": "C"},
    {"id": 88, "difficulty": "hard", "question": "Solve using substitution: (x+y)/2 - (x-y)/3 = 8, (x+y)/3 + (x-y)/4 = 11", "options": {"A": "x=10, y=6", "B": "x=12, y=4", "C": "x=14, y=2", "D": "x=16, y=0"}, "correct_answer": "B"},
    {"id": 89, "difficulty": "hard", "question": "Solve using substitution: 3x - 4y = 7, 5x + 2y = 3", "options": {"A": "x=1, y=-1", "B": "x=2, y=-0.25", "C": "x=3, y=0.5", "D": "x=4, y=1.25"}, "correct_answer": "A"},
    {"id": 90, "difficulty": "hard", "question": "Solve using substitution: 2/(x+1) + 3/(y-1) = 2, 4/(x+1) - 9/(y-1) = -1", "options": {"A": "x=1, y=4", "B": "x=2, y=3", "C": "x=3, y=2", "D": "x=4, y=1"}, "correct_answer": "A"},
    {"id": 91, "difficulty": "hard", "question": "Solve using substitution: 0.3x + 0.4y = 2.5, 0.5x - 0.2y = 0.9", "options": {"A": "x=1, y=5.5", "B": "x=2, y=4.75", "C": "x=3, y=4", "D": "x=4, y=3.25"}, "correct_answer": "C"},
    {"id": 92, "difficulty": "hard", "question": "Solve using substitution: 2x + 5y = 1, 6x + 15y = 4", "options": {"A": "x=0.5, y=0", "B": "x=1, y=-0.2", "C": "No solution", "D": "Infinitely many solutions"}, "correct_answer": "C"},
    {"id": 93, "difficulty": "hard", "question": "Solve using substitution: (x/4) + (y/5) = 1, (x/3) + (y/2) = 3", "options": {"A": "x=4, y=5", "B": "x=6, y=0", "C": "x=8, y=-5", "D": "x=12, y=-10"}, "correct_answer": "B"},
    {"id": 94, "difficulty": "hard", "question": "Solve using substitution: 4x + 8y = 12, 2x + 4y = 6", "options": {"A": "x=1, y=1", "B": "x=2, y=0.5", "C": "Infinitely many solutions", "D": "No solution"}, "correct_answer": "C"},
    {"id": 95, "difficulty": "hard", "question": "Solve using substitution: 5x - 3y = 11, 10x - 6y = 20", "options": {"A": "x=2, y=-0.33", "B": "x=3, y=1.33", "C": "No solution", "D": "Infinitely many solutions"}, "correct_answer": "C"},
    {"id": 96, "difficulty": "hard", "question": "Solve using substitution: (2x-1)/3 + (y+2)/4 = 4, (x+3)/2 - (y-1)/5 = 3", "options": {"A": "x=5, y=2", "B": "x=6, y=1", "C": "x=7, y=0", "D": "x=8, y=-1"}, "correct_answer": "A"},
    {"id": 97, "difficulty": "hard", "question": "Solve using substitution: 1.5x + 2.5y = 8.5, 0.5x + 0.5y = 2.5", "options": {"A": "x=1, y=4", "B": "x=2, y=3", "C": "x=3, y=2", "D": "x=4, y=1"}, "correct_answer": "B"},
    {"id": 98, "difficulty": "hard", "question": "Solve using substitution: 3(x+1) = 2(y-1), 5(x+2) = 3(y+1)", "options": {"A": "x=1, y=5", "B": "x=2, y=7", "C": "x=3, y=9", "D": "x=4, y=11"}, "correct_answer": "B"},
    {"id": 99, "difficulty": "hard", "question": "Solve using substitution: 0.2(x+3) - 0.3(y-2) = 1.1, 0.4(x-1) + 0.5(y+1) = 4.3", "options": {"A": "x=3, y=5", "B": "x=4, y=4", "C": "x=5, y=3", "D": "x=6, y=2"}, "correct_answer": "C"},
    {"id": 100, "difficulty": "hard", "question": "Solve using substitution: (3x-y)/5 = (x+y)/2 = 7", "options": {"A": "x=15, y=5", "B": "x=20, y=10", "C": "x=25, y=15", "D": "x=30, y=20"}, "correct_answer": "A"}
  ]
}