Number Systems-LCM & HCF

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sukhman: Master | Next Rank: 500 Posts; Posts: 202; Joined: Sun Sep 08, 2013 11:51 am; Thanked: 3 times; Followed by:2 members

Number Systems-LCM & HCF

by sukhman » Fri Oct 11, 2013 5:19 am

Least perfect square which is divisible by 3,4 ,6,8,10 and 11
Answer is 3*3*2*2*2*2*5*5*11*11
However my answer is 6 2s and not 4 2s

Last edited by sukhman on Fri Oct 11, 2013 6:21 am, edited 1 time in total.

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Source: Beat The GMAT — Problem Solving | Fri Oct 11, 2013 5:19 am

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by Brent@GMATPrepNow » Fri Oct 11, 2013 6:01 am

sukhman wrote:Least perfect square which is divisible by 3,4 ,6,8,10 and 11

Where are the answer choices?
In many instances, we can solve GMAT math questions quickly by using the answer choices to our advantage?

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

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by [email protected] » Fri Oct 11, 2013 1:03 pm

Hi sukhman,

The list of numbers that you're dealing with has some "overlap" among the numbers.

For example, anything that's divisible by 8 is ALSO divisible by 4 (so you can essentially ignore the 4 in your calculation).

If we prime factor this list, we'll have:

3 = 3
4 = 2x2
6 = 2x3
8 = 2x2x2
10 = 2x5
11 = 11

We need just ENOUGH prime factors to cover every item in this list:

We need: 2x2x2x3x5x11

The question asks for a perfect square, so we'd need to double the number of each:

2x2x2x2x2x2x3x3x5x5x11x11

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