Question

find the sum of natural numbers less than 100 which are divisible by seven

Answer 1

69.70.53.are the natural number is divisible by seven

Answer 2

AP for such numbers is 7,14,.............98

so, a =7 , d=7 
Let there be n terms in this AP

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

So, Sum = S14 = 14/2[a+l]
                          = 7[a+l]
                          = 7[7+98]
                          = 7[7+98]
                            7[105]
                           = 735