Question

The last term of the AP $21,18,15$ ....... is $-351$. Find the nth term.

• A. $213$
• B. $123$
• C. $312$
• D. $-231$

Answer 1

Answer: (B)

$123$

Given that, $a=21$; Last term$=-351,d=-3$
we know that, last term$=a+(n-1)d$
$-351=21-(n-1)3$
$-351=21-3n-3$
$-369=-3n$
$n=\frac{-369}{-3}$
$n=123$