Question

Find the sum of the first 15 multiples of 8.

Answer 1

Let the series be 8+16 .......... + 120
Here a = 8, d = 8, n = 15, l = 120

Sum = n/2(a+l)
Sum = 15/2(8+120)
= 15/2(128)
= 15 × 64
= 960


Thus sum of first 15 multiples of 8 = 960.

Answer 2

Hello,

Question;-

Find the sum of the first 15 multiplies of 8

Method of Solution;-


Let to be a is first term and 'd'" is common Difference and l is last term of Given Arithmetic Sequence or Progression;-

Arithmetic Sequence or Progression which are given below;-

Arithmetic Sequence or Progression;-

8,16,24,32....

Here,

First term= 8

CommOn Difference=8

Number of terms=15

We know that Formula of Summation of Arithmetic Sequence or Progression.

Sn=n/2(2a+(n-1)d)

S15=15/2(2x8+(15-1)8

  =15/2(16+(14)8)

  =15/2(16+112)

  =15/2 x 128

  =15 x 64

 =960


Hence ,960 are sum of the first 15 multiples of 8.