Question

find the sum of first 20 positive multiples of 7​

Answer 1

Answer:

7,14,21,..140 are first 20 terms

these are in AP

first term =a = 7

n= 20

d= a2-a1 = 14-7=7

last term = l=140

sum of n terms Sn = n/2 [a+last term]

s20 = 20/2[7+140]

=10*147

=1470