This is the Important question based on Arithmetic progression Chapter of R.S Aggarwal book for ICSE & CBSE Board.

Here you have to find the sum of first x multiples of given number.

Question Number 13 of Exercise 11 C of RS Aggarwal Solution

# Find the sum of first 15 multiples of 8.

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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(2×8+(15-1)8

=15/2(16+(14)8)

=15/2(16+112)

=15/2 x 128

=15 x 64

=960