Question

Find the sum of all two digit number greater than 50 .Which when divided by 7 leave reminder of 4

Answer 1

numbers greater than 50 which when divided by7 leaves remainder 4 starts from 53 then take common difference be 7 and make an AP.
53,60,67,74,81,88,95
A=53 d= 7 and An th term =95
find n and then put the formula of Sn = n/2(A+An)

Answer 2

53,60,67,75,.......95 he nth term is 95 common difference is 7 the first term is53 then Sn=n/2(2a+(n-1)d)
So sum of n terms=521