1.

If the arithmetic mean of the first n natural numbers is 15 , then n is `"__________"` .A. 15B. 20C. 14D. 29

Answer» Correct Answer - D
We have,
`(1+2+3+...+n)/(n)=15 rArr (n(n+1))/(2n)=15 rArr n = 29`


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