Question

Given the series 1+4+7+10+......Find the sum from 10th to 20th term

plz plz plz answer me..........​

Answer 1

Answer:

in the attachment ...pls refer

Answer 2

I. n=10, a=1, d=3

Sn= n/2[2a+(n-1)d]

S10= 10/2 [2(1)+(10-1)3]

= 5[2+(9)3]

= 5[2+27]

= 5[29]

= 145

II. n= 20

S20= 20/2[2(1)+(20-1)3]

= 10[2+(19)3]

= 10[2+57]

= 10[59]

= 590