Question

find the sum of first seven numbers which are multiples of 2 as well as 9

Answer 1

The sum of the first seven numbers which are multiples of 2 as well as 9 is 504.

Step-by-step explanation:

We have to find the sum of the first seven numbers which are multiples of 2 as well as 9.

The first number which is a multiple of 2 as well as 9 is 18. So, the series so formed is: 18, 36, 54, 72,......, and so on.

As here we can clearly see that the series form an A.P. because the common difference is the same between the terms, i.e. of 18.

Now, the sum to n terms of an A.P. is given by;

$S_n = \frac{n}{2}[2a+(n-1)d]$

Here, a = first term of AP = 18, d = common difference = 18 and n = 7 terms (because we have to find the sum if first seven numbers only).

So,  $S_7 = \frac{7}{2}[(2\times 18)+(7-1)\times 18]$

$S_7 = \frac{7}{2}[36+108]$

$S_7 = \frac{7}{2}[144]$

$S_7 =7 \times 72$

$S_7 =504$

Hence, the sum of the first seven numbers which are multiples of 2 as well as 9 is 504.

Answer 2

Step-by-step explanation:

Hope it will helps you....