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The sum of first five multiples of 3 is:

A. 45 B. 65 C. 75 D. 90 Answer: Option A
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Solution(By Apex Team)

$\begin{aligned}S_n&=[2a+(n-1)d]\times\frac{n}{2}\\ \Rightarrow S_5&=[2\times3+(5-1)3]\times\frac{5}{2}\\ \Rightarrow S_5&=[6+12]\times\frac{5}{2}\\ \Rightarrow S_5&=18\times\frac{5}{2}\\ \Rightarrow S_5&=9\times5\\ &=45\end{aligned}$

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