There are 200 questions in a 3 hour examination. Among these questions are 50 mathematical problems. It is suggested that twice as much time be spent on each mathematical problem as for each other question. How many minutes should be spent on mathematical problems?

Let x = time for each non-math problem, so 2x = time for each math problem. Total: 150×x + 50×2x = 180 minutes. This gives 150x + 100x = 180, so 250x = 180, and x = 0.72 minutes. Time for 50 math problems = 50 × 2x = 100 × 0.72 = 72 minutes. Note: This requires interpreting 'among these questions are 50 mathematical problems' as meaning 150 other + 50 math = 200 total, not 200 + 50.