Time taken to produce widgets

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gmattesttaker2: Legendary Member; Posts: 641; Joined: Tue Feb 14, 2012 3:52 pmFollowed by: 8 members; Thanked: 11 times

by gmattesttaker2 » Sun May 25, 2014 9:04 pm

Hello,

For the following:

If Machine X can produce 80 widgets in 4 hours, how long would it take machine X and Y working together, to produce 500 widgets?

1.Machine Y works at 3/4 the speed of machine X
2.If Machine Y's speed doubled, it would produce 120 widgets in 4 hours

OA: D

Machine X produces 20 widgets per hour. Does Statement 1 mean that Machine Y's speed is 3/4(20) = 15 widgets per hour?

Thanks a lot,
Sri

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Source: Beat The GMAT — Data Sufficiency | Sun May 25, 2014 9:04 pm

theCodeToGMAT: Legendary Member; Posts: 1556; Joined: Tue Aug 14, 2012 11:18 pmFollowed by: 34 members; Thanked: 448 times; GMAT Score:650

by theCodeToGMAT » Sun May 25, 2014 9:24 pm

X = 80 widgets = 4 hr ==> 1hr = 20 W

X & y together =500

We need to find Y's speed

Statement 1:
Y = 3/4 * X
We can get Y's speed
SUFFICIENT

Statement 2:
2 * y = 120 W in 4 Hr
SUFFICIENT

[spoiler]{D}[/spoiler]

R A H U L

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theCodeToGMAT: Legendary Member; Posts: 1556; Joined: Tue Aug 14, 2012 11:18 pmFollowed by: 34 members; Thanked: 448 times; GMAT Score:650

by theCodeToGMAT » Sun May 25, 2014 9:29 pm

gmattesttaker2 wrote:Hello,

Machine X produces 20 widgets per hour. Does Statement 1 mean that Machine Y's speed is 3/4(20) = 15 widgets per hour?

Yes!

R A H U L

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GMAT/MBA Expert

ceilidh.erickson: GMAT Instructor; Posts: 2095; Joined: Tue Dec 04, 2012 3:22 pmFollowed by: 247 members; Thanked: 1443 times

by ceilidh.erickson » Mon May 26, 2014 7:36 am

gmattesttaker2 wrote:Does Statement 1 mean that Machine Y's speed is 3/4(20) = 15 widgets per hour?

The answer is... it doesn't matter! Because this is a DS question, you don't actually have to do the math here.

First, figure out what your target question really is:

Given: If Machine X can produce 80 widgets in 4 hours, how long would it take machine X and Y working together, to produce 500 widgets?

Infer: If we know X's time and output, then we know X's rate: 80/4. If we want to know the time it would take X and Y working together, then we need Y's rate.

1.Machine Y works at 3/4 the speed of machine X
Don't waste time doing the math here! We know X's rate, so we can use this to get a value for Y's rate. Then we would be able to add X's and Y's together and solve for the time - but we don't need to actually do that!

2.If Machine Y's speed doubled, it would produce 120 widgets in 4 hours
If we are given information about twice Y's rate, then we can solve for Y's rate. Once again, don't actually do that math!

The answer is D.

Ceilidh Erickson
EdM in Mind, Brain, and Education
Harvard Graduate School of Education

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