In the afternoon, a student read 100 pages at the rate of 60 pages / hour. In the evening, when he was tired, he read 100 more pages at the rate of 40 pages/hour. What was his average rate of reading in pages per hours?

Calculate the weighted average of reading speeds. In the afternoon: 100 pages at 60 pages/hour = 100/60 = 5/3 hours. In the evening: 100 pages at 40 pages/hour = 100/40 = 5/2 hours. Total pages = 200, total hours = 5/3 + 5/2 = (10+15)/6 = 25/6 hours. Average speed = Total pages / Total hours = 200 ÷ (25/6) = 200 × (6/25) = 8 × 6 = 48 pages/hour. Option A is correct.