Question

Find the 20th term of an AP whose 7th term is 24 less than the 11th term, first term being 12.

Answer 1

Given ,

First term $=a=12$

Let the common difference be $d$

and we know 7th term $a_7=a+6d$

and 11th term $a_{11}=a+10d$

According to question ,

$a_{11}-a_7=24$

$a+10d-(a+6d)=24$

$a+10d-a-6d=24$

$4d=24$

$d=6$

We know that,

20th term $=a_{20}=a+19d=12+19\left(6\right)=12+114=126$

So , the 20th term of AP is 126.