Question

The first and last term of an A.P. are $1$ and $11$. If the sum of its terms is $36$, then the number of terms will be

• A. $5$
• B. $6$
• C. $7$
• D. $8$

Answer 1

The correct option is B $6$

$a=1a+(n-1)d=111+(n-1)d=11(n-1)d=10$

Also, Sum $=\frac{[a+(a+(n-1)d\left)\right]}{2}n$

$\Rightarrow 36=n\times \frac{12}{2}$

$\Rightarrow n=6$