Question

If the mean of first n natural numbers is 3n/5, then the value of n is:
(a)3
(b)4
(c)5
(d)6​

Answer 1

Answer:

(d)6

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Answer 2

sum of n natural no. = n(n+1)/2

mean of n natural no. = n(n+1)/2n = (n+1)/2

•°• (n+1)/2= 3n/5

=>5(n+1)=6n

=>5n+5=6n

=>5n-6n= -5

=> -n= -5

=>n = 5