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## printer A and printer B

This topic has 1 expert reply and 5 member replies
nhai2003 Rising GMAT Star
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printer A and printer B Fri Jul 10, 2009 10:45 pm
Elapsed Time: 00:00
• Lap #[LAPCOUNT] ([LAPTIME])
Working together, printer A and printer B would finish the task in 24 minutes. Printer A alone would finish the task in 60 minutes. How many pages does the task contain if printer B prints 5 pages a minute more than printer A ?
1:600
2:800
3:1000
4:1200
5:1500

Help me!

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brick2009 Really wants to Beat The GMAT!
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Fri Jul 10, 2009 11:17 pm
The answer should be : A

A+B = x/24 pages/min
A = x/60 pages/min
B = (x/60 + 5) pages/min

x/24 = x/60 + (x/60 + 5)
x/24 - 2x/60 = 5
Solve for X , X = 600

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Fri Jul 10, 2009 11:28 pm
good one.Thanks

we can calculate,B alone can do in 40 mins

Now say its 600

A--10(60)=600

B---15(40)=600

Together--25(24)=600

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samirnajeeb Just gettin' started!
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Sun Jan 02, 2011 5:11 am
time taken by A & B working together = a*b/(a+b)

60b/(60+b)=24
b=40
b takes 40mins to complete the task

B in a minute=x/40
A in a minute=x/60

x/40-x/60=5

x=600

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GMATGuruNY GMAT Instructor
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Sun Jan 02, 2011 5:20 am
nhai2003 wrote:
Working together, printer A and printer B would finish the task in 24 minutes. Printer A alone would finish the task in 60 minutes. How many pages does the task contain if printer B prints 5 pages a minute more than printer A ?
1:600
2:800
3:1000
4:1200
5:1500

Help me!
We can plug in the answer choices, which represent the number of pages. The correct answer choice will be divisible by 24 and 60. Eliminate B, C and E.

Combined rate for A+B = w/t = 600/24 = 25 pages per minute.
Rate for A alone = w/t = 600/60 = 10 pages per minute.
Rate for B alone = Combined rate - A alone = 25-10 = 15 pages per minute.
Difference between B and A = 15-10 = 5 pages per minute. Success!

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mcdesty Rising GMAT Star
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Tue Apr 10, 2012 12:13 pm
Rate Time Distance
Printer A a/60 60 a (Question then becomes what is A?)

Printer B (a/60)+5 (B prints 5 pages a minute more than printer A)

Together = a/60 + (a/60)+5
= a/60 + (a/60) + (300/60) (Same as 5)
= a/60 + (300 + a)/60 (Add them now as they have a common denominator)
= (2a + 300)/60 (Combined Rate)
= a/(2a + 300)/60 = 24 (This is how we got 24;By dividing the distance/combined rate)
= 60a = 24(2a +300) (Algebra, be careful here!!)
= 60a - 48a= 24(300) (Do not simplify until the very end:You just waste time by doing so)
= a= 600
I think this is faster!

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Tue Apr 10, 2012 9:24 pm
nhai2003 wrote:
Working together, printer A and printer B would finish the task in 24 minutes. Printer A alone would finish the task in 60 minutes. How many pages does the task contain if printer B prints 5 pages a minute more than printer A ?
1:600
2:800
3:1000
4:1200
5:1500

Help me!
AO must be multiple of 60. (bcoz d combined time taken is a whole number)

Lets start with 600 (on actual GMAT its better to start with B or D rather than starting with extremes A or D)

A= 600/60 = 10 units of work
B= 10+ 5= 15 units of work

combined units of work done in a minute = 25 (10+15 A+B)
Combined Time taken = total work/combined rate = 600/25 = 24 which is given in the question. Hence AO= A.

GMAT Quant tip on work rate:
Always assume the work done as LCM of the individual rates.
Benefits:
1. Avoid fractions in calculations and hence avoid calculation mistakes.
2. Saves few seconds. (do not undermine the few seconds saved on EACH Question)

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