[{"id": 1, "type": "short_answer", "skill": "addition", "question": "Calculate: 91 + 139", "difficulty": "medium", "explanation": "Add by place value, regrouping as needed.", "needs_review": false, "correct_answer": "230"}, {"id": 2, "type": "multiple_choice", "skill": "addition", "options": ["229", "230", "240", "235"], "question": "What is the sum of 91 and 139?", "difficulty": "easy", "explanation": "91+139=230", "needs_review": false, "correct_answer": "230"}, {"id": 3, "type": "true_false", "skill": "properties", "question": "The commutative property means 91+139 = 139+91.", "difficulty": "easy", "explanation": "The commutative property states changing the order of addends does not change the sum.", "needs_review": false, "correct_answer": "True"}, {"id": 4, "type": "short_answer", "skill": "computation", "question": "Calculate: 19 × 8", "difficulty": "medium", "explanation": "Multiply: 19×8=152", "needs_review": false, "correct_answer": "152"}, {"id": 5, "type": "short_answer", "skill": "computation", "question": "Calculate: 10 × 4", "difficulty": "medium", "explanation": "Multiply: 10×4=40", "needs_review": false, "correct_answer": "40"}, {"id": 6, "type": "short_answer", "skill": "computation", "question": "Calculate: 11 × 8", "difficulty": "medium", "explanation": "Multiply: 11×8=88", "needs_review": false, "correct_answer": "88"}, {"id": 7, "type": "short_answer", "skill": "computation", "question": "Calculate: 3 × 3", "difficulty": "medium", "explanation": "Multiply: 3×3=9", "needs_review": false, "correct_answer": "9"}, {"id": 8, "type": "short_answer", "skill": "computation", "question": "Calculate: 10 × 14", "difficulty": "medium", "explanation": "Multiply: 10×14=140", "needs_review": false, "correct_answer": "140"}]