Rishi got the following marks on four math tests: $71,77,80$, and 87 . He will write one more math test. Each test is worth the same amount and all marks are between 0 and 100. Which of the following is a possible average for his five math tests?
(A) 88
(B) 62
(C) 82
(D) 84
(E) 86
The sum of Rishi's marks so far is $71+77+80+87=315$.

Since Rishi's mark on his next test is between 0 and 100, the sum of his marks will be between $315+0=315$ and $315+100=415$ after his next test.

Since his average equals the sum of his marks divided by the number of marks, then his average will be between $\frac{315}{5}=63$ and $\frac{415}{5}=83$.

Of the given choices, the only one in this range is 82 .

ANswer: (C)