Q. 195.0( 5 Votes )
Given: numbers which are multiples of 2 as well as of 9.
To find: S7
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
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]
Hence the required sum is 504
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