Question

For the given sequence $21,16,11,6,1\dots$, which term is equal to $-54$?

• A. $8$
• B. $12$
• C. $16$
• D. $20$

Answer 1

The correct option is C $16$

Given : $21,16,11,6,1\dots$
As $16-21=11-16=1-6=-5$, so the sequence is A.P. with $a=21,d=-5$
Now,
$T_n=a+(n-1)d\Rightarrow -54=21+(n-1)(-5)\therefore n=16$