Concept:  The question tests on Rates

Solution:

Let the total time taken to read = t

80M + 100D = t ... (1) and

50M + 250D = t ... (2)

Time taken to read 80 math pages and 100 drawing pages = time taken to read 50 math pages and 250 drawing pages.

80M + 100D = 50M + 250D

30M = 150D

Or D = 30/150=1/5 M

Substituting in equation (1), 80M + 100 * 1/5 M = 80M + 20M = 100M

So he can read 100 math pages in the given period of time.

 Option C