Question

The algebraic form of an arithmetic sequence is 4n+2. The numbers of terms required to get the sum as 880

• A. -20
• B. 20
• C. -22
• D. 22

Answer 1

The correct option is B

20

Sum of n terms $=\frac{an(n+1)}{2}+bn$

$=\frac{4n(n+1)}{2}+2n$

=2n(n+1)+2n

$=2n^2+2n+2n$

$=2n^2+4n$

Now for sum to be 880

$2n^2+4n=880$

$2(n^2+2n)=880$

$n^2+2n=440$

$n^2+2n-440=0$

$n^2+22n-20n-440=0$

n(n+22)-20n-440=0

$\Rightarrow n+22=0$ or n-20=0

$\Rightarrow n=-22$ or n=20

No of terms cannot be -ve so n=20