Question

the mean of first n numbers is 5n/9. then n is

Answer 1

this is the correct form

Answer 2

Arithmetic mean of first n numbers -
sum of total numbers / n

Sum of the first n natural numbers =
$\frac{n(n + 1)}{2}$
Now the question reduces to

$\frac{n + 1}{2} = \frac{5n}{9} \\ 9(n + 1) = 2(5n) \\ n = 9$
Hence n = 9