Question

which term of the AP 3,15,27,39 is 120 more then 21

Answer 1

Given AP :- 3, 15, 27, 39, ..........

Here, a = 3.

d = 15-3 = 12.

First. we will obtain the 21st term.  

By using formula, an = a + (n -1)d

a21 = 3 + (21 -1)12

= 3 + 20 × 12

= 3 + 240

= 243.

Hence, the 21st term of the AP is 243.

Now, term that is 120 more than 21st term will be

--> a21 + 120

--> 243 + 120

--> 363.