Question

Let S be the sum of the first n terms of the arithmetic sequence 8, 12, 16, .....……., and T be the sum of first n terms arithmetic sequence 17, 19, 21, ….......….. . If $S-T=0$, then the value of n is equal to

• A. 8
• B. 10
• C. 18
• D. 22

Answer 1

Answer: (B)

$S=\frac{n}{2}[16+4(n-1)];T=\frac{n}{2}[34+2(n-1)]$
$\therefore S-T=0\Rightarrow 16+4n-4=34+2n-2\Rightarrow 4n+12=32+2n\Rightarrow 2n=20\Rightarrow n=10$