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

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Sum

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

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#### Solution

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 ….

Here, first term (a) = 18,

Common difference d) = 36 – 18 = 18

∵ S_n = n/2 [2a + (n - 1)d]

S_7 = 7/2 [2(18) + (7 - 1)8]

= 7/2[36 + (6 xx 18)]

= 7(18 + 3 xx 18)

= 7(18 + 54)

= 7 xx 72

= 504

Concept: Sum of First n Terms of an A.P.
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#### APPEARS IN

NCERT Mathematics Exemplar Class 10
Chapter 5 Arithematic Progressions
Exercise 5.3 | Q 31 | Page 54
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