Question

13. Find the sum of the first 15 multiples of 8.
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Answer 1

First 15 multiples of 8 = 8,16,24,32,40,48,56,64,72,80,88,96,

104,112, 120

Now,sum = 960

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Answer 2

Answer:

a = 8

n = 15

d = 8

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

= 15/2 (2×8 + (14)8]

= 15/2 [16 +112]

= 15/2 [128]

= 15 [64]

= 960