The mean of 1^3, 2^3, 3^3, 4^3, 5^3, 6^3, 7^3 is

SSC CGL 30 Aug 2015 Paper

Question : 143 of 200

Marks: +1, -0

The mean of

1^3, 2^3, 3^3, 4^3, 5^3, 6^3, 7^3

Solution:

Sum of the cubes of first n natural numbers
=

({n(n+1)}/2)^3

Their average =

{n(n+1)^2}/4

∴ Required average when n = 7,
=

{7(7+1)^2}/4

{7×8×8}/4

= 112

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