Working together, printer A and printer B would finish the : Problem Solving (PS)

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Working together, printer A and printer B would finish the

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Manager

Joined: 12 Jul 2018

Posts: 67

Location: India

Schools: ISB '20, NUS '21

GMAT 1: 420 Q26 V13

GMAT 2: 540 Q44 V21

Re: Working together, printer A and printer B would finish the [#permalink]

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11 Dec 2018, 11:40

gauravnagpal wrote:

Spoiler: ::

I know this question is relatively symol if make an equation in one vaibale ...
I tried to do it by applying the fundamental of A = Jobs per min * time ( the way we typically solve the work problems ) and i was stuck

I did jobs per minute A , 1/60
combined rate = 1/24

so rate of b = 1/24 - 1/60 = 1/40

but could not arrive at the solution ... i tried to form the equation by assuming x as the total numbe of pages So x/60+ x+5/40 = cld nt take ot forward from here
kindly see where am I losing the track !

Solution by Bunuel as per the GMAT Club Math Book

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Re: Working together, printer A and printer B would finish the [#permalink]

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15 Dec 2018, 09:20

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 ?

A. 600
B. 800
C. 1000
D. 1200
E. 1500

POE approach :
we are given combined time= 24
ie combined rate per minute= 1/24

s the time here is an integer then the whole work must be divisible by 24 ...or we wont get an integer value
eliminate all the choices that are not divisible by 24 ...
choices B C E gone

between choices A and D i would straight away choose option A 600 because A takes only 60 minutes to complete the work... now even if you are not sure
try to divide with individual rates and you will see A is the answer choices

TAKEAWAY:
- Use POE when you are running out of time...the above appraoch took me less than 45 seconds... all you have to do is increase your probability of answering the Q correctly...your probability after eliminating 3 choices becomes 50%..
- thumbrule - the huge the amount of work the more the time required...as the time taken is not very considerable then so will the work be...not too great...

Trust me i try this appraoch when I'm at 28th Q , and have to rush...i use this this appraoch n guess what i alnost get 50% answers right...thats better than answering just 1 right and randomly guessing other

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Joined: 27 Nov 2015

Posts: 42

Re: Working together, printer A and printer B would finish the [#permalink]

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06 Feb 2019, 02:31

In this case we'd have:
The rate of printer A = 1/a pages per minute, where a is the time to print 1 page.
The rate of printer B = 1/b pages per minute, where b is the time to print 1 page.

Working together, printer A and printer B would finish the task in 24 minutes" --> \(24(\frac{1}{a}+\frac{1}{b})=x\);
Printer A alone would finish the task in 60 minutes --> \(60*\frac{1}{a}=x\);
Printer B prints 5 pages a minute more than printer A --> \(\frac{1}{b}=\frac{1}{a}+5\).

Solving for \(x\) --> \(x=600\).

Answer: A.[/quote]

Can I get some help please? In some questions, we put the completed task as "1" however in this case we put the pages (completed task) as x... why is that the case? How can i know when to use "1" and when to use a variable?