Question

Which term of the AP $24,21,18,..............$ is the first negative term. ?

• A. 8th
• B. 9th
• C. 10th
• D. 12th

Answer 1

The correct option is C 10th

Since the series is divisible by 3,

$\therefore$ The first -ve term = -3

$\therefore$ ATP

$a=24$

$d=21-24=-3$

$\therefore T_n=a+(n-1)d$

$\Rightarrow -3=24+(n-1)(-3)$

$\Rightarrow (n-1)\left(3\right)=27$

$\Rightarrow n-1=9$

$\therefore n=10$

(Ans: 10th term $\to$ C)