1.  (51 + 52 + 53 + ... + 100) = ?
A. 2525
B. 2975
C. 3225
D. 3775

Answer: Option D

Explanation:

This is an A.P. in which a = 51, l = 100 and n = 50.

Sum = n (a + l) = 50 x (51 + 100)   
2 2

= (25 x 151)   = 3775.