Question

find the sum of 15 multiples of 4

Answer 1

sum of 15 multiples of 4 :
4 + 8 +12 +16 +20 +24 + 28 +32 +36 +40 +44 +48 +52 +56 + 60
480
is your answer..

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Answer 2

$\underline{\Large\mathbf{Question}}$

$\bf Sum \: of \: first \: 15 \: multiples \: 4$

$\underline{\underline{\huge\mathfrak{Solution}}}$

Formula used :

$\boxed{\boxed{\large\mathbf{S = \frac{n}{2} ( 2a + (n - 1) d)}}}$

Since, we have to find the sum of $\bf multiples$ of 4,

a = 4
And also, $a_{2} = 8$
d (Common Difference) = $a_{2} - a_{1}$
d = 8 - 4 i.e. 4
n (Number of terms) = 15

Putting the values in the formula we get,

$S_{15} = \frac{15}{2} (2(4) + (15 - 1)4) \\ \\ S_{15} = \frac{15}{2} (8 + (14)(4)) \\ \\ S_{15} = \frac{15}{2} (8 + 56) \\ \\ S_{15} = \frac{15}{2} \times 64 \\ \\ S_{15} = 15 \times 32 \\ \\ \bf S_{15} = 480$

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