please I need an answer to this one

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Sharbel: Junior | Next Rank: 30 Posts; Posts: 17; Joined: Sat Mar 08, 2008 5:51 am; Location: Saudi Arabia

please I need an answer to this one

by Sharbel » Thu Apr 17, 2008 8:11 am

In the figure below, segments RS and TU represent two positions of the same ladder leaning against the side SV of a wall. The length of TV is how much greater than the length of RV?

(1) The length of TU is 10 meters.
(2) The length of RV is 5 meters.

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Sharbel Nasr

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Source: Beat The GMAT — Data Sufficiency | Thu Apr 17, 2008 8:11 am

simplyjat: Master | Next Rank: 500 Posts; Posts: 423; Joined: Thu Dec 27, 2007 1:29 am; Location: Hyderabad, India; Thanked: 36 times; Followed by:2 members; GMAT Score:770

by simplyjat » Thu Apr 17, 2008 8:29 am

(1) The length of TU is 10 meters. SUFFICIENT
TV = TU * cos 45
RV = TU * cos 60

(2) The length of RV is 5 meters.
TU = RV / cos 45
TV = TU * cos 45

The essence of question is to understand TU = RS

simplyjat

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Sharbel: Junior | Next Rank: 30 Posts; Posts: 17; Joined: Sat Mar 08, 2008 5:51 am; Location: Saudi Arabia

by Sharbel » Thu Apr 17, 2008 11:34 am

The first part of TV= TU cos 45 is simple , i can get that using pythagore but the second part is not clear, how did you calculate that RV=TU cos 60 and since you are saying R,V,T,U that means 4 points no longe a triangle !!!??? please explain

thanks

Last edited by Sharbel on Thu Apr 17, 2008 11:46 am, edited 1 time in total.

Sharbel Nasr

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Stuart@KaplanGMAT: GMAT Instructor; Posts: 3225; Joined: Tue Jan 08, 2008 2:40 pm; Location: Toronto; Thanked: 1710 times; Followed by:614 members; GMAT Score:800

by Stuart@KaplanGMAT » Thu Apr 17, 2008 11:37 am

Sharbel wrote:WOOOOOW

cos45 !!!!

didn't even cross my mind

all the reviewing i made so far concentrated on Pythagor and a few other simple rules about triangles.

no mention of the cos and sin until now, i was completely blind to it.

thanks simplyjat i really needed this pointer

now i will go review the cos and sin properties

STOP!! :!:

This is a data sufficiency question. In other words, we don't need to actually calculate the answer, we merely need to see if the answer is attainable.

You WILL NOT need to know trigonometry for the GMAT.

We could have answered this question by using 30/60/90 and 45/45/90 pythagorean triplets. You DO need to know those two special right triangles.

Stuart Kovinsky | Kaplan GMAT Faculty | Toronto

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Sharbel: Junior | Next Rank: 30 Posts; Posts: 17; Joined: Sat Mar 08, 2008 5:51 am; Location: Saudi Arabia

by Sharbel » Thu Apr 17, 2008 11:54 am

Stuart Kovinsky wrote:
Sharbel wrote:WOOOOOW

cos45 !!!!

didn't even cross my mind

all the reviewing i made so far concentrated on Pythagor and a few other simple rules about triangles.

no mention of the cos and sin until now, i was completely blind to it.

thanks simplyjat i really needed this pointer

now i will go review the cos and sin properties
STOP!! :!:

This is a data sufficiency question. In other words, we don't need to actually calculate the answer, we merely need to see if the answer is attainable.

You WILL NOT need to know trigonometry for the GMAT.

We could have answered this question by using 30/60/90 and 45/45/90 pythagorean triplets. You DO need to know those two special right triangles.

I hear you stuart,

but still i need to know the answer, i have this question from some DS sets downloaded from this forum, i answered C but the right answer according to the answer sheet is D, i need the solution to understand how each statement is sufficient alone. Thanks

Sharbel Nasr

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netigen: Legendary Member; Posts: 631; Joined: Mon Feb 18, 2008 11:57 pm; Thanked: 29 times; Followed by:3 members

by netigen » Thu Apr 17, 2008 1:24 pm

Remember that TU = RS since it's the same ladder and hence the Ans is D

Since from (A) we know TU and hence also know RS
from (B) we know RV so we can calculate RS and so also get TU

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Stuart@KaplanGMAT: GMAT Instructor; Posts: 3225; Joined: Tue Jan 08, 2008 2:40 pm; Location: Toronto; Thanked: 1710 times; Followed by:614 members; GMAT Score:800

by Stuart@KaplanGMAT » Thu Apr 17, 2008 1:44 pm

We know a LOT about the situation: the relative length of the ladders (the same, since it's the same ladder) and the dimensions of each triangle. The only thing we're missing is an actual measurement.

So, pretty much any measurement relevant to either triangle will let us solve for every last little part of the system.

Each of (1) and (2) gives us a measurement. As soon as we recognize that all we need is one such length, we can see that each one will be sufficient on its own.