Question

Which term of the AP 4, 12, 20, 28, .... will be 120 more than its 21st term ?

Answer 1

Here,

$a=4,d=8$

Therefore, $a_{21}=a+20d=4+20\times 8=164$

Let the nth term be the required term.

$nthterm=120+21stterm$

$a+(n-1)d=120+164$

$4+(n-1)8=284$

$(n-1)8=280$

$n-1=35$

$n=36$

Therefore, 36th term, i.e., 284 will be 120 more than its 21st term.