Question

If the first term of an A.P. be 10, last term is 50 and the sum of all the terms is 300, then the number of terms are [RPET 1987]
A) 5 B) 8 C) 10 D) 15

Answer 1

300=n/2*{10+50/2}.
15n=300
n=300/15
=20

Answer 2

Therefore the answer is 10.