Certain type of question (Official Guide)

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bff7942: Newbie | Next Rank: 10 Posts; Posts: 7; Joined: Thu Feb 14, 2008 2:18 pm

by bff7942 » Sun Mar 02, 2008 1:30 am

Is there some kind of rule to this?

OG DS139- If x=/=y, is (x-y)/(x+y)>1?
OG DS 143- If m>0 & n>0, is (m+x)/(n+x)>m/n?
OG DS 145- Is 1/p > r/ (r^2 + 2)?

I tried to eliminate some variables by re-writing the inequalities, but seems like that's not the right way to solve the problem. I know it works for some other problems? How do you know when you should eliminate variables and when you should not?

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Source: Beat The GMAT — Data Sufficiency | Sun Mar 02, 2008 1:30 am

nutreino: Junior | Next Rank: 30 Posts; Posts: 11; Joined: Thu Feb 28, 2008 10:20 am

by nutreino » Sat Mar 08, 2008 10:53 am

Most of the times elimination of variable works to get the answer. Some times you need to reframe the inequalities to make it looks simpler.

Eg:
139: (!= --- means not equal to)
x!=-y => x+y!=0
After which try substituting NGP numbers and check for various combinations.

145:
This also can be written as:
pr/(r^2+2)<1
- check with option 1 and NGP values for r
- now check with only positive value.

BOTTOMLINE: Try to simplify a complicated looking inequality to simpler looking one. If elimination isnt as obvious, dont waste time to dig it out. Check with NGP numbers (substituting single digit numbers wont take longer).

Hope it helps!

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hengirl03: Senior | Next Rank: 100 Posts; Posts: 86; Joined: Tue Aug 05, 2008 10:50 am; Thanked: 7 times

by hengirl03 » Tue Aug 19, 2008 10:41 am

What do you mean by NGP?

nutreino wrote:Most of the times elimination of variable works to get the answer. Some times you need to reframe the inequalities to make it looks simpler.

Eg:
139: (!= --- means not equal to)
x!=-y => x+y!=0
After which try substituting NGP numbers and check for various combinations.

145:
This also can be written as:
pr/(r^2+2)<1
- check with option 1 and NGP values for r
- now check with only positive value.

BOTTOMLINE: Try to simplify a complicated looking inequality to simpler looking one. If elimination isnt as obvious, dont waste time to dig it out. Check with NGP numbers (substituting single digit numbers wont take longer).

Hope it helps!

Like this post

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