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
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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