Question

The sum of given A.P.1, 4 , 7 , 10 , . . . upto 20 terms is____________ .

Answer 1

Answer:

Given AP is 1,4,7,10,.....

In given AP first term a=1, common difference d=3

Since, Sn= n/2[2a+(n−1)d] ....... sum of n terms

Put n=20 for sum of first 20 terms

S20=20/2 [2(1)+(20−1)3]

S20=10[2+57]

S20=590