Question

sum of integers from 1 to 100 which are divisible by 7 from 50 to 100 is

Answer 1

We have to find Sum of integers from 50 to 100 which are divisible by 7.

So, AP is 56,..............98 

Here, a = 56, d = 7
Let there be n terms in this AP so an = 98

56+ (n-1)d = 98
56+ (n-1)7 = 98
       n-1 = 6
       n= 7
       

So, S = S7 = 7/2 [a+l]
                     = 7/2[56+98]
       
                     = 7[28+49]
                     = 7*77
                     = 539