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OG problem 5.5.29 - quicker method?

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OG problem 5.5.29 - quicker method?

by bekkilyn » Tue Oct 14, 2008 3:39 pm
OG problem 5.5.29

I'm able to do this problem and get the correct answer, but it seems that there is a lot of calculation and so I'm wondering if there is a trick to getting it done faster.

The method I used was to multiply and then add each pair of numbers under the square root, and separate all the square factors. Then I take the square root of those squares and multiply those remaining numbers together for the answer.

It works, but it seems like it takes a long time to get it done. Am I using the most efficient way of solving this problem?
Last edited by bekkilyn on Tue Oct 14, 2008 4:37 pm, edited 1 time in total.
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Re: OF problem 5.5.29 - quicker method?

by Stuart@KaplanGMAT » Tue Oct 14, 2008 4:21 pm
bekkilyn wrote:I'm able to do this problem and get the correct answer, but it seems that there is a lot of calculation and so I'm wondering if there is a trick to getting it done faster.

The method I used was to multiply and then add each pair of numbers under the square root, and separate all the square factors. Then I take the square root of those squares and multiply those remaining numbers together for the answer.

It works, but it seems like it takes a long time to get it done. Am I using the most efficient way of solving this problem?
No clue to which problem you're referring!
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by bekkilyn » Tue Oct 14, 2008 4:38 pm
It didn't help that I had a typo in the subject line.

It's for OG problem 5.5.29
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by cramya » Tue Oct 14, 2008 5:16 pm
Bekki,
Please take this as a request. Kindly post the problem as not everyone on this forum may have the og and even if they did the time to refer to the problem and then provide the solution.

I am sure that this is the problem you are referring to:

sqrt[(16*20)+(8*32)]

In this probelm if we simplify whats inside the square we get

sqrt[320+256]
sqrt[576]
= 24

Friendly tip: Its good thing to know the squares for GMAT for atleast numbers till 25.

Hope this helps! Good luck!
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by bekkilyn » Tue Oct 14, 2008 5:22 pm
So far then, memorization would seem to be the quickest way for this one. :)

I would be happy to post the OG problems when asking for help on them, but I thought posting the actual OG problem text was illegal? Or does that only apply to the Manhattan GMAT forums and nowhere else?
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by Gmatss » Tue Oct 14, 2008 5:26 pm
well recognize to get 6 unit digit on a perfect square it's either 6x6 or 4x4
so u can also try to plug in answers with 6 or 4 unit digit and get the answer
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