Question

a=90 , d=20, find the sum of 20th term.

Answer 1

Howdy!!

your answer is --

Given, a = 90 & d = 20

therefore
S20 = 20/2 [2a + 19d]
= 10[ 2×90+19×20]
= 10[560] = 5600

hope it help you_____

Answer 2

First term = a = 90
Last term =20th term
Last term = a+19d =90+19(20)
Last term = 90+380
Last term = 470

Now,

Sum of n term = n/2 [last term+ first term]

Here,

Sum of 20 term = 20/2 [470+90]

Sum of 20 terms =10×560

Sum of 20 term = 5600



I hope this will help you

-by ABHAY