geometry problem

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adwaitkasbekar: Junior | Next Rank: 30 Posts; Posts: 16; Joined: Sun Nov 14, 2010 11:01 pm

by adwaitkasbekar » Wed Dec 22, 2010 12:50 am

Can some one please explain how to solve this problem?

In isosceles triangle RST, what is measure of angle r?
a. Angle T is 100Âº
b. Angle S is 40Âº

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Source: Beat The GMAT — Data Sufficiency | Wed Dec 22, 2010 12:50 am

Night reader: Legendary Member; Posts: 1337; Joined: Sat Dec 27, 2008 6:29 pmFollowed by: 10 members; Thanked: 127 times

by Night reader » Wed Dec 22, 2010 1:02 am

adwaitkasbekar wrote:Can some one please explain how to solve this problem?

In isosceles triangle RST, what is measure of angle r?
a. Angle T is 100Âº
b. Angle S is 40Âº

simply it's choice A! you may eliminate the other two angles, since 100+2x=180 and 100*2>180 st(1) Sufficient
st(2) we may have 40-40-100 or 40-70-70 Not Sufficient

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Rahul@gurome: GMAT Instructor; Posts: 1179; Joined: Sun Apr 11, 2010 9:07 pmFollowed by: 88 members; Location: Milpitas, CA; Thanked: 447 times

by Rahul@gurome » Wed Dec 22, 2010 2:03 am

adwaitkasbekar wrote:In isosceles triangle RST, what is measure of angle r?
a. Angle T is 100Âº
b. Angle S is 40Âº

Given: RST is an isosceles triangle. That means it has two equal angles and the third one is different. Now angle R may be one of the equal angles or the different one.

Statement 1: Angle T = 100Âº
As T > 90Âº, there is no way T is one of the equal angles. Thus R and S must be the equal angles. Which implies 2R = (180Âº - T) = (180Âº - 100Âº) = 80Âº => R = 40Âº

Sufficient.

Statement 2: Angle S = 40Âº
As S < 90Âº, S may be one of the equal angles or may be the different one.

Not sufficient.

The correct answer is A.

Rahul Lakhani
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Gurome, Inc.
https://www.GuroMe.com
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adwaitkasbekar: Junior | Next Rank: 30 Posts; Posts: 16; Joined: Sun Nov 14, 2010 11:01 pm

by adwaitkasbekar » Thu Dec 23, 2010 3:04 am

thank rahul......that was simple enough.

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