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A computer chip manufacturer expects the ratio of the number

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vinubala
 Post subject: A computer chip manufacturer expects the ratio of the number
 Post Posted: Sun Aug 03, 2008 2:34 am 
Source: GMATPrep Practice Test

A computer chip manufacturer expects the ratio of the number of defective chips to the total number of chips in all future shipments to equal the corresponding ratio for shipments S1, S2, S3 and S4 combined, as shown in the below table. What is the expected number of defective chips in the shipment of 60,000 chips?
1. 14
2. 20
3. 22
4. 24
5. 26

(Shipment) --- Number of Defective Chips --- Total Number of Chips
in the Shipment in the Shipment

S1 --- 2 --- 5,000
S2 --- 5 --- 12,000
S3 --- 6 --- 18,000
S4 --- 4 --- 16,000
Top 
RA
 Post subject:
 Post Posted: Sun Aug 03, 2008 9:21 pm 
Defects in X chips = defects per chip * X

S1 + S2 + S3 + S4 = 17 defects in 51,000 chips or 1 defect in 3000 chips or 1/3000 defects per chip

defects in 60,000 chips = 1/3000 * 60,000 = 20

Answer is B (20)

Hope that helps
Top 
ii
 Post subject:
 Post Posted: Fri Aug 22, 2008 7:35 pm 
Or you can setup a proportion to solve this.

Let N=number of defective chips in the shipment of 60000. The number which we are trying to find.

N/60000 = 2+5+6+4 / 5000 + 12000+18000 + 16000

N/60000 17/51000

cross multiply this proportion:

51000N = 1020000
51N = 1020
N = 1020/51
N = 20.
Top 
RonPurewal
 Post subject:
 Post Posted: Wed Oct 29, 2008 7:43 am 
Offline
ManhattanGMAT Staff


Posts: 7146
excellent answers.
Top 
rudransh
 Post subject: Re:
 Post Posted: Tue Nov 29, 2011 6:26 pm 
Offline
Students


Posts: 3
RonPurewal wrote:
excellent answers.


Ron,

How the below two are different? When to use which one, well I ended up using later and ended up taking a big calculation....but that brought up this question, when to use later option?

2+5+6+4 / 5000 + 12000+18000 + 16000

versus

2/5000 + 5/12000 + 6/18000 + 4/16000

??
Top 
tarunlakhani
 Post subject: Re: A computer chip manufacturer expects the ratio of the number
 Post Posted: Fri Dec 02, 2011 12:16 pm 
Offline
Students


Posts: 3
God! I have no clue what is dis question talking abt? Is GMAT quant language always so twisted?

Please help me understand dis ques
Top 
jnelson0612
 Post subject: Re: Re:
 Post Posted: Sun Dec 25, 2011 11:33 pm 
Offline
ManhattanGMAT Staff


Posts: 1857
suniltomar_personal wrote:
RonPurewal wrote:
excellent answers.


Ron,

How the below two are different? When to use which one, well I ended up using later and ended up taking a big calculation....but that brought up this question, when to use later option?

2+5+6+4 / 5000 + 12000+18000 + 16000

versus

2/5000 + 5/12000 + 6/18000 + 4/16000

??


Let's use some much easier numbers to illustrate why you can't do what you are suggesting.

Let's say that I have 2 + 4 + 6/8 + 12 + 18. That is 12/38, or 6/19.

2/8 + 4/12 + 6/18 is 1/4 + 1/3 + 1/3, or 3/12 + 4/12 + 4/12=11/12. Not the same.

Thus, what you are suggesting is not a good move because it will not give you the same result.

_________________
Jamie Nelson
ManhattanGMAT Instructor
Top 
jnelson0612
 Post subject: Re: A computer chip manufacturer expects the ratio of the number
 Post Posted: Sun Dec 25, 2011 11:38 pm 
Offline
ManhattanGMAT Staff


Posts: 1857
tarunlakhani wrote:
God! I have no clue what is dis question talking abt? Is GMAT quant language always so twisted?

Please help me understand dis ques


Basically a chip maker assumes that a certain part of the total number of chips that he produces will be defective. He thinks that the percent defective in all the chips he makes will be equal to the percentage defective in the total group of the chips made up by batches 1, 2, 3 and 4. Does this help?

_________________
Jamie Nelson
ManhattanGMAT Instructor
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