inequality

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tanviet: Legendary Member; Posts: 1404; Joined: Tue May 20, 2008 6:55 pmFollowed by: 2 members; Thanked: 18 times

by tanviet » Fri Oct 30, 2009 5:56 am

this is from 15 testset

n>0, which is greater, 20 percent of n or 10 percent of the sum of n and 0.5

a,n<0.1
b,n>0.01

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Source: Beat The GMAT — Data Sufficiency | Fri Oct 30, 2009 5:56 am

NikolayZ: Master | Next Rank: 500 Posts; Posts: 124; Joined: Thu Jun 18, 2009 5:33 am; Thanked: 35 times

by NikolayZ » Fri Oct 30, 2009 6:19 am

Hey Duongthang!

we need to know which is greater : 0.2n or 0.1n+0.05

From 1) n<0.1. let's plug in even 0.1, yo my mind it doesn't matter here : to plug in 0.1,0.095 or 0.01.

0.2*0.1=0.02, whereas 0.1*0.1+0.05=0.051. Hence 0.02<0.051 - Sufficient.
(you can do it yourself with another variables, such as 0.01 or whatever. The whole inequality won't change)

From 2) Here, we need to notice that n is positive, and if it is >0 but <0.1, the right part of inequality is greater.
when it is >0.1, we get the following:
0.2*0.2=0.04
and
0.1*0.2+0.05=0.09, still sufficient.
finally, plug in 0.9
0.2*0.9=0.18
and
0.1*0.9+0.05=0.09+0.05=0.14. left part becomes greater that the right.
Hence 2) - insufficient.

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punitkaur: Master | Next Rank: 500 Posts; Posts: 168; Joined: Mon Apr 13, 2009 6:48 pm; Thanked: 6 times

by punitkaur » Fri Oct 30, 2009 6:47 am

According to me the answer should be C and not A.

Which is greater 0.2n or 0.1n+0.05

Let x=0.2n, y=0.1n+0.05

A) Given n<0.1

Therefore x<0.02 , y<0.06

Using the above inequalities

a)if x=0.01, y=0.01 ,y=x.
b)if x=0.01, y=0.02 , y>x

INSUFFICIENT to say which is greater

B) Given n>0.01

Therefore x >0.002, y>0.051
a)if x = 0.052, y=0.052 , y=x
b)if x=0.051, y=0.052, y>x

INSUFFICIENT

C) Considering A & B together
0.002 < x < 0.02
0.052 < y < 0.06

y > x SUFFICIENT

Hence C

Whats the OA?

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NikolayZ: Master | Next Rank: 500 Posts; Posts: 124; Joined: Thu Jun 18, 2009 5:33 am; Thanked: 35 times

by NikolayZ » Fri Oct 30, 2009 7:28 am

Oops.
Sorry for disinformation. I don't why, but i even did not check a couple of possible numbers <0.1 =(
Thank you Punitkaur.
Indeed the answer is C.

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ayashlaha: Junior | Next Rank: 30 Posts; Posts: 10; Joined: Sun Oct 25, 2009 2:09 pm; Thanked: 2 times

by ayashlaha » Fri Oct 30, 2009 10:11 am

I still think that the answer is A

In Punit Kaur's example:

if X=0.01 then n = 0.05
If n=0.05 then Y=0.055

Hence Y is greater.

In my mind I would rewrite the problem statement as:
is 0.2n = 0.1n + 0.05
=> Is 0.1n = 0.05

this is only true if n =0.5

However it is stated that n< 0.1 , hence statement 1 is sufficient.

Stetement 2 by itself is inconclusive if n is a large integer number.

Please post official answer or alternate explaination if you think I'm wrong.

Thanks.

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