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Arithmetic Progressions
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02/06/2021 10:35 am
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Find the sum of first 40 positive integers divisible by 6.
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02/06/2021 10:36 am
The positive integers that are divisible by 6 are 6, 12, 18, 24 ….
First term is 6 and common difference is 6.
a = 6
d = 6
S40 = ?
Sn = n/2 [2a +(n – 1)d]
Therefore, putting n = 40, we get,
S40 = 40/2 [2(6)+(40-1)6]
= 20[12+(39)(6)]
= 20(12+234)
= 20×246
= 4920