Question

Using AP find sum of all 3 digit no. Divisible by 7

Answer 1

3 Digit Numbers divisible by 7 are as follows: 105, 112, ......, 994

a = 105
an = 994
d = 112 - 105 = 7

an = a + (n - 1)d

994 = 105 + (n - 1)7

(n - 1)7 = 994 - 105

(n - 1)7 = 889

n - 1 = 889/7

n - 1 = 127

n = 128

Sn = (n/2)*(a + an)

S128 = (128/2)*(105 + 994)

S128 = (64)*(1099)

S128 = 70336 ——> Answer