Question

I m having a doubt that is the question I have done is correct or not... plz check &let me know..

Answer 1

Multiples of 8 are 8,16,24,32...Which forms an AP.

Let a be the first term and d be the common difference.

first term a = 8

common difference d = 16 - 8

                                     = 8

n = 15.


We know that sum of n terms of an AP = n/2(2a + (n - 1) * d)

                                                                  = 15/2(2(8) + (15 - 1) * 8)

                                                                  = 15/2(16 + 14 * 8)

                                                                  = 15/2(128)

                                                                  = 15 * 64

                                                                  = 960.


Therefore the sum of first 15 multiples of 8 = 960.


Hope this helps!