In afternoon, a student read 100 pages at rate of 60 pages per hour. In evening, when she was tired, she read 100 more pages at rate of 40 pages per hour. What was her average rate of reading pages per hours ?

According to the question,
Afternoon
100 pages read at the rate 60 pages per hour
Total time taken to read 100 pages
= $$\frac{100}{60}$$
= $$\frac{5}{3}$$ hours

Evening
100 pages read at the rate 40 pages per hour
Total time taken to read 100 pages
= $$\frac{100}{40}$$
= $$\frac{5}{2}$$ hours
Average rate of reading the pages per hour
$$\eqalign{ & = \frac{{200}}{{\frac{5}{3} + \frac{5}{2}}} \cr & = \frac{{200 \times 6}}{{10 + 15}} \cr & = \frac{{200 \times 6}}{{25}} \cr & = 48 \cr} $$