Sum of Cube

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dtweah: Master | Next Rank: 500 Posts; Posts: 487; Joined: Fri Mar 27, 2009 5:49 am; Thanked: 36 times

by dtweah » Tue May 05, 2009 3:06 am

What is the sum of the cube of the first 20 positive integers?

A. 20000

B. 30100

C. 40200

D. 44100

E. 48400

Source: Beat The GMAT — Problem Solving | Tue May 05, 2009 3:06 am

gauravgundal: Master | Next Rank: 500 Posts; Posts: 199; Joined: Mon Apr 06, 2009 4:15 am; Location: India; Thanked: 13 times

by gauravgundal » Tue May 05, 2009 3:31 am

Answer : D

Sum of cube of first n natural numbers = [n^2*(n+1)^2]/4
n=20

Last edited by gauravgundal on Tue May 05, 2009 3:52 am, edited 1 time in total.

deepoe: Master | Next Rank: 500 Posts; Posts: 151; Joined: Wed Feb 11, 2009 2:45 am; Thanked: 3 times

by deepoe » Tue May 05, 2009 3:37 am

what did you filled in for N?

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