DS on inequalities

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r_walid
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Topic: DS on inequalities
PostTue Nov 03, 2009 8:22 pm Reply with quote
IF material A cost 3$/kg and B cost 5$/kg.
If 10 kg of material K conssit of x kg of A and y kg of B, is x>y?

1- y>4

2- the cost of 10kg of K is less than $40.
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PostTue Nov 03, 2009 9:06 pm Reply with quote
r_walid wrote:
IF material A cost 3$/kg and B cost 5$/kg.
If 10 kg of material K conssit of x kg of A and y kg of B, is x>y?

1- y>4

2- the cost of 10kg of K is less than $40.
IMO D

the question can be rephrased as is x>5?

1. if y>4 then x = 5, 4,3, 2, 1. in all cases it is not more than y hence suff.

2. 3x + 5(10-x) < 40 -> 10<2x -> x<5 -> suff

hope that helps.
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venubab
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PostWed Nov 04, 2009 1:10 am Reply with quote
Answer B

1. y>4

Say, y=4.1, x=5.9 x>y
Say, y=6, x=4 x<y

Not sufficient

B is sufficient
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PostFri Nov 06, 2009 11:10 pm Reply with quote
r_walid can you please post the OA.

thanks.
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okigbo
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PostTue Nov 17, 2009 12:01 pm Reply with quote
life is a test: how can A be sufficient if we dont know the total cost? I think it is B - two equations / two unknowns
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PostTue Nov 17, 2009 4:19 pm Reply with quote
life is a test wrote:
r_walid wrote:
IF material A cost 3$/kg and B cost 5$/kg.
If 10 kg of material K conssit of x kg of A and y kg of B, is x>y?

1- y>4

2- the cost of 10kg of K is less than $40.
IMO D

the question can be rephrased as is x>5?

1. if y>4 then x = 5, 4,3, 2, 1. in all cases it is not more than y hence suff.

2. 3x + 5(10-x) < 40 -> 10<2x -> x<5 -> suff

hope that helps.
Statement 1 says y>4. So, y can be 4.2. Then x will be 5.8. So, x>y. Now, y can also be 8, since 8 is greater than 4.
Then x will be 2. So here y > x.
Hence statement 1 is not sufficient.

Statement 2 as you all know is very sufficient.
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palvarez
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PostTue Nov 17, 2009 10:51 pm Reply with quote
okigbo wrote:
life is a test: how can A be sufficient if we dont know the total cost? I think it is B - two equations / two unknowns
Master this problem. You gonna see similar problems on GMAT: at least two or three.


It is a weighted avg problem.

A's average: 3, B's average: 5
The mixture's average < 4


When you combine A and B equally, the average gonna be 4.

When the average < 4. Then we can say that A's quantity < B's quantity.


Look at a generalization: You are given a list of n numbers.

The lowest in that list <= average <= the largest.

In these questions, don't waste your time setting up all algebraic equations, etc. If you notice the pattern, answering this question would take a couple of seconds.
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beatthegmat2910
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PostThu Nov 19, 2009 4:19 pm Reply with quote
IMO D.
Condition 1 - Y > 4; y=5,6,7,8,9
x=5,4,3,2,1

x=y for one set ,hence Not sufficient.

Condition 2-
3x+5y < 40 ; This is also not sufficient , since 3x+5y could be anything under 40.

Combining 1 and 2 , the only value that 3X+5Y can hold so that Condition 1 is true is 39.
Solving the two equations, you get the answer.
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