Q19 of 38 Page 5

Find the sum of first seven numbers which are multiples of 2 as well as of 9.

Given: numbers which are multiples of 2 as well as of 9.


To find: S7


Formula Used:


Sum of “n” terms of an AP:



Where Sn is the sum of first n terms


n = no of terms


a = first term


d = common difference


Explanation:


For finding, the sum of first seven numbers which are multiples of 2 as well as of 9.


Take LCM of 2 and 9 which is 18.


So, the series becomes 18, 36, 54, ….


Clearly this series is an AP.


Here, first term, a = 18


common difference, d = 36 – 18 = 18


Now as Sum of first n terms of an AP is




= 7[ 18 + 54]


= 504


Hence the required sum is 504


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