Question

Find the sum of first 8 multiples of 3

Answer 1

First, 8 multiples of 3 are { 3, 6, 9...,24}

We can observe they are in AP with first term (a) = 3 and last term (l) = 24 and number of terms are 8.

`S_n = n/2 (a + l)`

`=> S_n = 8/2(3 + 24)`

`S_8 = 4 xx (3 + 24) = 108`

Hence, the sum of the first 8 multiples of 3 is 108

 

Answer 2

First 8 multiples of 3 are

3, 6, 9, 12, 15, 18, 21, 24

The above sequence is an A.P

a= 3, d= 3 and last term l = 24

`S_n = n/2 (a + 1) = 8/2[3 + 24] = 4(27)`

`S_n = 108`