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Machines X and Y run at different constant rates

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Machines X and Y run at different constant rates

by nhai2003 » Mon Jul 13, 2009 11:28 pm
Machines X and Y run at different constant rates, and machine X can complete a certain job in 9 hours. Machine X worked on the job alone for the first 3 hours and the two machines, working together, then completed the job in 4 more hours. How many hours would it have taken machine Y, working alone, to complete the entire job?
18
13+1/2
7+1/5
4+1/2
3+2/3

Guys please help
Thanks in advance!
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by zenithexe » Tue Jul 14, 2009 12:17 am
There is is, it will look confusing if I written it here so its a pic file

hope it helps.

Just noticed, some sentence errors. Please ignore typos/bad grammar lol
Attachments
RateofXY.jpg
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by nhai2003 » Tue Jul 14, 2009 12:45 am
Thanks zenithexe you rocks!!!
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My way

by rangerguy2000 » Tue Jul 14, 2009 9:06 am
Let Job=36
Rate (x)=36/9=4 parts/hr
Rate (y)=36/y
x works for 3 hrs, means 4*3=12 (x did 12 parts of the job)
SO, remaining Job=36-12=24
Now, x works at the rate of 4 parts/hr, so x works for 4 hrs, means,
x did 4*4=16 parts of the job,
So, remaining job is 24-16=8.
Now, Rate (y)=8/4=2 parts/hr.
So y will take 36/2=18 hrs to complete the full (36) job.

Hope it makes sense.
Always try to pick a number for the job, to make it easier to work with.
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