Question

find the sum of two digit number which are divisible by7

Answer 1

Lets form the AP

AP:- 14,21,28..........98

Therefore,
a=14
d=7
an=98

an= a + (n-1) × d
98= 14 + (n-1) ×7
98-14= 7n - 7
84= 7n - 7
84+7= 7n
91= 7n
91/7= n
n=13

Sn = n/2 (a+an)
Sn = 13/2 (14+98)
Sn = 13/2 (112)
Sn = 6.5 (112)
Sn = 728

=>The sum 2 digit numbers which are divisible by 7 are 728