Question

Which term of the AP 3,15, 27, 39, ... will be 120 more than its 21st term

Answer 1

Answer:

The 31st term of the AP will be 120 more than the 21st term.

Step-by-step explanation:

From the given data,

a = 3 , d = 15 - 3 = 12

a21 = a + 20d

= 3+20×12 = 3+240 =243

So, an = 243 + 120 = 363

Now, 363 = a +(n-1)d

=> 363 = 3+ 12n -12

=> 363 + 9 = 12n

=> n = 372/ 12

= 31