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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

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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Many of the great achievements of the world were accomplished by tired and discouraged men who kept on working.

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

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!

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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Vinoth@GMAT Kolaveri
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