absolute values

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pink_08: Senior | Next Rank: 100 Posts; Posts: 87; Joined: Wed Dec 31, 2008 7:01 pm

by pink_08 » Fri Mar 12, 2010 11:35 pm

I saw this property in one of the DS questions -

x=-3y This tells us X and Y have different signs. ( -,+)

we can also say |x| = 3|y|

Which number property does the above reflect ? Are n't we forgetting the negative sign by converting to absolute value ?

Pls clarify

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Source: Beat The GMAT — Data Sufficiency | Fri Mar 12, 2010 11:35 pm

Phirozz: Master | Next Rank: 500 Posts; Posts: 232; Joined: Sun Feb 28, 2010 10:47 pm; Thanked: 10 times

by Phirozz » Sat Mar 13, 2010 12:24 am

pink_08 wrote:I saw this property in one of the DS questions -

x=-3y This tells us X and Y have different signs. ( -,+)

we can also say |x| = 3|y|

Which number property does the above reflect ? Are n't we forgetting the negative sign by converting to absolute value ?

Pls clarify

After converting both sides are +ve. So it does not matter whether sign of x and y are +ve or -ve. We are concerned about onl absolute values

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pink_08: Senior | Next Rank: 100 Posts; Posts: 87; Joined: Wed Dec 31, 2008 7:01 pm

by pink_08 » Sat Mar 13, 2010 8:31 pm

Can you please explain in detail. I'm still missing a few pieces here.

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sarthak: Senior | Next Rank: 100 Posts; Posts: 75; Joined: Tue Jan 19, 2010 10:43 am

by sarthak » Mon Mar 15, 2010 9:51 pm

this |number| is known as mod . If you use this operand it means strip off the sign and just be concerned about the absolute value.

eq. x=3 y= -3

so x is not equal to y

but x =|y| because thier absolute values is 3 is same .

I hope you are clear now. In case of further doubt pls lemme kno

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kevincanspain: GMAT Instructor; Posts: 613; Joined: Thu Mar 22, 2007 6:17 amFollowed by: 64 members; Location: madrid; Thanked: 171 times; GMAT Score:790

by kevincanspain » Tue Mar 16, 2010 2:35 am

pink_08 wrote:I saw this property in one of the DS questions -

x=-3y This tells us X and Y have different signs. ( -,+)

we can also say |x| = 3|y|

Which number property does the above reflect ? Are n't we forgetting the negative sign by converting to absolute value ?

Pls clarify

Remember that if two numbers are equal, their absolute values (distances from zero) are equal. (The reserve, however, is not always true)

The absolute value of a product of two terms is the product of the absolute values of the two terms.
In short, |ab| =|a| |b|

Thus |-3y| = |-3| |y| = 3|y|

Kevin Armstrong
GMAT Instructor
Gmatclasses
Madrid

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