Help---question from Princeton GMAT Math Bible

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amyyoung999: Junior | Next Rank: 30 Posts; Posts: 11; Joined: Mon Dec 08, 2008 4:39 pm

by amyyoung999 » Thu Dec 18, 2008 10:16 pm

I encounter a very similiar question as this one from Princeton GMAT Math
Bible.
The instruction on the book using the formula to slove this question
Can any body teach me the formula.

the question is

1+2^2+3^2+4^2+.....................9^2+10^2=?

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Source: Beat The GMAT — Problem Solving | Thu Dec 18, 2008 10:16 pm

EmilKhalikov: Newbie | Next Rank: 10 Posts; Posts: 9; Joined: Wed Dec 17, 2008 8:30 pm; Thanked: 2 times

by EmilKhalikov » Fri Dec 19, 2008 9:17 am

1 + 2 + 3 + ... + n = n(n+1)/2
1^2 + 2^2 + ... + n^2 = n(n+1)(2n+1)/6
1^3 + 2^3 + ... + n^3 = ( n^2(n+1)^2 )/4

I cannot believe they would ask such question. If you do not remember the formulas, you are pretty much screwed because it is nearly impossible to figure out those formulas.

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amyyoung999: Junior | Next Rank: 30 Posts; Posts: 11; Joined: Mon Dec 08, 2008 4:39 pm

by amyyoung999 » Fri Dec 19, 2008 12:07 pm

Thank you very much!
I encountered this question when I took the test last month,and my friend
encountered the same question this week.

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EmilKhalikov: Newbie | Next Rank: 10 Posts; Posts: 9; Joined: Wed Dec 17, 2008 8:30 pm; Thanked: 2 times

by EmilKhalikov » Fri Dec 19, 2008 12:17 pm

Here is more:
1 + 3 + 5 + ... + (2n - 1) =n^2
2 + 4 + 6 + ... + 2n = n*(n+1)
1^2 + 3^2 + ... + (2n-1)^2 = n(4n^2 - 1)/3
1^3 + 3^3 + ... + (2n-1)^3 = n^2(2n^2 - 1)

Combining these formulas with the ones I posted earlier should help calculating various integer series

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amyyoung999: Junior | Next Rank: 30 Posts; Posts: 11; Joined: Mon Dec 08, 2008 4:39 pm

by amyyoung999 » Fri Dec 19, 2008 3:16 pm

Wow!You are an elite on Math.
You must hold a PH.D from department of Mathematics.
Thanx a lot!

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EmilKhalikov: Newbie | Next Rank: 10 Posts; Posts: 9; Joined: Wed Dec 17, 2008 8:30 pm; Thanked: 2 times

by EmilKhalikov » Fri Dec 19, 2008 8:27 pm

Lol no, I am Applied Math major and I am pretty good at it, so I figure I help other people. It's a good practice for me too.

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amitabhprasad: Master | Next Rank: 500 Posts; Posts: 259; Joined: Thu Jan 18, 2007 8:30 pm; Thanked: 16 times

by amitabhprasad » Sat Dec 20, 2008 1:04 am

@ amyyoung999
do you mean you go this test in GMATPrep questions ?

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amyyoung999: Junior | Next Rank: 30 Posts; Posts: 11; Joined: Mon Dec 08, 2008 4:39 pm

by amyyoung999 » Sat Dec 20, 2008 6:32 am

This question is from Princeton GMAT Math Bible.
I relize that the questions on the Princeton GMAT Math Bible are much more difficult than the questions on GMATPREP.

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