Question

Find the number of multiple of 9 lying between 300 and 700.​

Answer 1

Answer:

Here series will be = 306, 315, 324, 333,...........693

So we have the first term a = 306 and d = 9 and last term l = 693

693 = 306 + (n-1)9

77 = 34 + (n-1)

n = 77 - 34 +1

  = 44

Sum = n/2(a+l)

       = 44/2(306+693)

       = 22(999)

       = 21978.

Hope this helps!