Question

The sum of the first four terms of an A.P. is 56. The sum of the last four terms is 112. If its first term is 11, the number of terms is.

• A. 10
• B. 11
• C. 12
• D. None of these

Answer 1

Answer: (B)

11

Answer 2

$11 + ( 11 + d ) + ( 11 + 2 d ) + ( 11 + 3 d ) = 56$ $\Rightarrow$ $d = 2$

and $\{ 11 + ( n - 1 ) 2 \} + \{ 11 + ( n - 2 ) 2 \}$

$+ \{ 11 + ( n - 3 ) 2 \} + \{ 11 + ( n - 4 ) 2 \} = 112$

$\Rightarrow$ $n = 11$.