The sum of first five multiples of 3 is


The first five multiples of 3 are 3, 6, 9, 12 and 15.


Here, first term, a = 3, common difference, d = 6 – 3 = 3 and number of terms, n = 5


Using the formula,



Where Sn is the sum of first n terms


n = no of terms


a = first term


d = common difference


S5 = (5/2)[ 2(3) + (5 - 1)(3)]


= (5/2)[ 6 + 12]


= 5(9)


= 45

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