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D.S.

by vladmire » Wed Dec 03, 2008 4:06 pm
I still don't seem to understand how I can use (2) to figure out the length of the longer piece.

A wooden rod is cut into two pieces. What is the length of the longer piece?

(1) One of the pieces is 20 inches longer than the other piece
(2) The length of the shorter piece is 1/3 the length of the longer piece

a. first
b. second alone
c. both together
d. each one alone
e. neither
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Source: — Data Sufficiency |
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by earth@work » Wed Dec 03, 2008 4:52 pm
i think we need some more info to solve this... something missing!
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hmmm.

by vladmire » Wed Dec 03, 2008 5:14 pm
OA=C

Thats all the information they give me
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by earth@work » Wed Dec 03, 2008 6:02 pm
i think i got it!
1) let the length of shorter piece be x, then longer piece will be (x+20)
Total will be 2x+ 20....this is all we get from stmnt 1..insufficient
(2) The length of the shorter piece is 1/3 the length of the longer piece
we get smaller piece as total length/4 & longer length=3(total length)/4 .. this is insufficient
(1)+(2) from (1) we get total length = 2x+20
from (2) we get 1/4 of total length = smaller piece=(2x+20)/4
smaller piece from(1)=x
x=(20+2x)/4
x=10
longer piece =10*2+20=40
answer C
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by cramya » Wed Dec 03, 2008 7:31 pm
Not a big deal but I think shorter piece is 10 and longer piece 30

Still C)
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by vishubn » Thu Dec 04, 2008 1:58 am
Ya same Line ! this is a fraction problem ! in the first statement u get the difference in length and connected thru a unknown term x

Second statement u get ! 1/3 which is the relation again bet ween

So we use both we get the length

Straight forward indeed

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by vish150783 » Thu Dec 04, 2008 11:56 am
two variables, two equatioons.. :evil:
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by Stuart@KaplanGMAT » Thu Dec 04, 2008 1:28 pm
vish150783 wrote:two variables, two equatioons.. :evil:
This rule is, without a doubt, THE most powerful tool for solving data sufficiency questions.

If you understand the "n distinct linear equations for n variables" rule (including all of its subtleties), you will save a TON of time in data sufficieny.

Let's see how quickly we could have solved this question:

Q: Cut a rod into two pieces (we'll call them l and s). How long is l?

(1) l is 20 more than s.

We can make this into one equation, but we have two unknowns: insufficient.

(2) s is 1/3 l.

We can make this into one equation, but we have two unknowns: insufficient.

Together: two distinct linear equations, two unknowns. We can answer ANY question about the system: sufficient.

Together sufficient, apart insufficient: choose (C).

Note that not only did we not solve for l, but we also didn't even bother to translate the equations. Avoiding unnecessary calculations is the key to DS happiness.
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