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.

• A. 5
• B. 8
• C. 10
• D. 15

Answer 1

Answer: (C)

10

Answer 2

Given that first term $a = 10$ , last term $l = 50$ and sum $S = 300$

$\therefore S = \frac { n } { 2 } ( a + l )$ $\Rightarrow$ $300 = \frac { n } { 2 } ( 10 + 50 )$ $\Rightarrow$ $n = 10$ .