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If Max can complete a job in 4...

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If Max can complete a job in 4...

by Layo » Tue Sep 14, 2010 7:02 am
Greetings everyone, I`m newbie at gmat DS and have problem with this task. Could you help me solve it.

If Max can complete a job in 4 hours and Nick can complete the same job in 6 hours, how many fewer hours do Max and NIck working together need to complete the job than Max alone need to complete the job?

A. 1.6
B. 2.4
C. 3.2
D. 3.4
E. 5.0
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by kvcpk » Tue Sep 14, 2010 7:12 am
First correction. This is a PS problem and not a DS problem.

I request the moderator to move it to the right forum.

Anyways, Here is the approach.

Whenevr you are given such problems, you will first need to find the LCM of the numbers that you seein the problem.

Numbers are 6 and 4. LCM is 12.

Now, assume there is 12 units of work.

Max completes in 4 hours. So He does 12/4 = 3 units per hour.
Nick completes in 6 hours. So He does 12/6 = 2 units per hour.
Therefore Together, they do 3+2 = 5 units per hour.

We have total of 12 units. So they can complete the task in 12/5 Hours = 2.4 hours.

Question is asking how many fewer hours are needed than Max alone doing it.

Max does in 4 hours. So difference = 4-2.4 = 1.6 hours.

pick A.

Hope this helps!!
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don't be afraid of failure and don't abandon it.
People who work sincerely are the happiest."
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by Layo » Tue Sep 14, 2010 7:24 am
Thanks, kvcpk! Hope someday i can solve such problems as quick as you.
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by kvcpk » Tue Sep 14, 2010 7:30 am
Layo wrote:Thanks, kvcpk! Hope someday i can solve such problems as quick as you.
The method I used is a kind of shortcut because it reduces complex calculations using Fractions. Practice this on couple of more problems and I am sure you will master this approach.

Only difference between you and me is I did such problems earlier and you did not. Now we both are equal. :)

Cheers!!
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by beatthegmatinsept » Tue Sep 14, 2010 7:44 am
@ kvcpk - Quick question, why did you assume 12 units of work? Are you purposely picking a number that's a factor of both 4 and 6 to make calculation easier?
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by kvcpk » Tue Sep 14, 2010 7:50 am
beatthegmatinsept wrote:@ kvcpk - Quick question, why did you assume 12 units of work? Are you purposely picking a number that's a factor of both 4 and 6 to make calculation easier?
Exactly. Take LCM of the numbers you see. So that you can divide easily.
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don't be afraid of failure and don't abandon it.
People who work sincerely are the happiest."
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by beatthegmatinsept » Tue Sep 14, 2010 7:58 am
kvcpk wrote:
beatthegmatinsept wrote:@ kvcpk - Quick question, why did you assume 12 units of work? Are you purposely picking a number that's a factor of both 4 and 6 to make calculation easier?
Exactly. Take LCM of the numbers you see. So that you can divide easily.
That's a smart approach. I usually solve such problems taking 'x' as the job, but substituting 'x' with '12' here makes it less prone to calculation errors.
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by selango » Tue Sep 14, 2010 8:00 am
Another similar approach.

Max:A-->1 job in 4 hrs or 1/4th job in 1 hr

Nick:B-->1 job in 6 hrs or 1/6th job in 1 hr

1 hr=1/A+1/B=1/6+1/4=10/24

=24/10 hrs or 2.4 hrs

Difference=4-2.4=1.6 hrs
--Anand--
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