Question

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

Answer 1

tn=t21+120
4+(n-1) 8=4+(21-1) 8+120
(n-1) 8=280
n=36

Answer 2

Answer:

36 th term of given A.P will be 120 more than its 21st term

Step-by-step explanation:

Given A.P: 4,12,20,28,...

First term (a)=4

Common difference (d)=a2-a1

= 12-4

= 8

Let nth term of given A.P ,will be 120 more than its 21st term

$a_{n}=a_{21}+120$

$\implies a+(n-1)d=a+(21-1)d+120$

$\implies a+(n-1)d=a+20d+120$

$\implies (n-1)d=20d+120$

$\implies (n-1)8=20\times 8+120$

$\implies (n-1)8 = 160+120$

$\implies (n-1)8=280$

$\implies (n-1)=\frac{280}{8}$

$\implies n= 35+1$

$\implies n = 36$

Therefore,

36 th term of given A.P will be 120 more than its 21st term

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