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Arithmetic Progressions
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02/06/2021 10:37 am
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Find the sum of first 15 multiples of 8.
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02/06/2021 10:38 am
The multiples of 8 are 8, 16, 24, 32…
First term as 8 and common difference as 8.
a = 8
d = 8
S15 = ?
Sn = n/2 [2a+(n-1)d]
S15 = 15/2 [2(8) + (15-1)8]
= 15/2[6 +(14)(8)]
= 15/2[16 +112]
= 15(128)/2
= 15 × 64
= 960