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If the arithmetic mean of the first n na...

If the arithmetic mean of the first n natural numbers is 15 , then n is `"__________"` .

A

15

B

20

C

14

D

29

Text Solution

Verified by Experts

The correct Answer is:
D
We have,
`(1+2+3+...+n)/(n)=15 rArr (n(n+1))/(2n)=15 rArr n = 29`
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