Question

mean of first natural numbers is 20 then n=

Answer 1

Sum of first 'n' natural numbers= n*(n+1)/2
For eg: 1+2+3=6 (n=3,n-1=2, sum= 3*2=6)
Mean = sum/number of quantities
Mean = n*(n+1)/2*n = n+1/2
Given,mean=20
(n+1)/2=20
n+1=40
n=39

Answer 2

mean = total sum of numbers / count of the numbers

sum of first 'n' natural number's = n*(n+1)/2

so mean = (n*(n+1)/2) /n = (n+1)/2 = 20

=> n = 39