Question:
Which term of the arithmetic progression 8, 14, 20, 26, ... will be 72 more than its 41st term.
Solution:
In the given problem, let us first find the 41st term of the given A.P.
A.P. is 8, 14, 20, 26 …
Here,
First term (a) = 8
Common difference of the A.P. $(d)=14-8=6$
Now, as we know,
$a_{v}=a+(n-1) d$
So, for 41st term (n = 41),
$a_{41}=8+(41-1)(6)$
$=8+40(6)$
$=8+240$
$=248$
Let us take the term which is 72 more than the 41st term as an. So,
$a_{v}=72+a_{41}$
$=72+248$
$=320$
Also, $a_{n}=a+(n-1) d$
$320=8+(n-1) 6$
$320=8+6 n-6$
$320=2+6 n$
$320-2=6 n$
Further simplifying, we get,
$318=6 n$
$n=\frac{318}{6}$
$n=53$
Therefore, the $53^{\text {rd }}$ term of the given A.P. is 72 more than the $41^{\text {st }}$ term.