A computer chip manufacturer expects the ratio of the number

[vinubala]

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

[RA]

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

[ii]

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.

[RonPurewal]

excellent answers.

[rudransh]

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

??

[tarunlakhani]

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

Please help me understand dis ques

[jnelson0612]

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.

[jnelson0612]

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?