Question
Find the sum of the first 15 multiples of 8.
Answer: Option B
:
B
The first 15 multiples of 8 are8, 16, 24, 32, .... 112, 120
First term, a=8
Common difference, d=16−8=8
n=15
Applying formula,Sn=n2(2a+(n−1)d) to findsum of n terms of AP,we get
S15=152(2(8)+(15−1)(8))
=152(16+8(14))
=152(16+112)
=152(128)=960
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:
B
The first 15 multiples of 8 are8, 16, 24, 32, .... 112, 120
First term, a=8
Common difference, d=16−8=8
n=15
Applying formula,Sn=n2(2a+(n−1)d) to findsum of n terms of AP,we get
S15=152(2(8)+(15−1)(8))
=152(16+8(14))
=152(16+112)
=152(128)=960
Was this answer helpful ?
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