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Question
Find the sum of the first 10 multiples of 6.
Solution
First 10 multiples of 6 are 6, 12, 18, 24, 30, 36, 42, 48, 54, 60.
This forms an AP with first term a = 6 and common difference, d = 6.
`"S"_"n" = "n"/2[2"a" +("n"-1)"d"]`
⇒ `"S"_10 = 10/2 [2xx6+(10-1)6]`
⇒ S10 = 5[12+54]
⇒ S10 = 5 × 66 =330
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