Question

Find the sum of multiples of 7 between 100 and 200?

Answer 1

AP: 105, 112, 119, .......196

First term of AP(a) = 105

Last term of AP(l) = 196

an=a+(n-1)d

196=105 +(n-1)7

196-105=7n-7

91=7n-7

98=7n

n=98/7

n=14

Sn=n/2(a+l)

Sn=14/2(105+196)

Sn=7×301

Sn=2107

Sum of multiples of 7 between 100 and 200 is 2107