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`