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# Tips and Hints for Specific Quant Topics (with Examples)

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Math Expert
Joined: 02 Sep 2009
Posts: 58402
Tips and Hints for Specific Quant Topics (with Examples)  [#permalink]

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Updated on: 26 Jul 2014, 16:13
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658

New project from GMAT Club

Tips and Hints for Specific Quant topics with Examples.
We will be posting 2 questions every week to illustrate common shortcuts and tips for solving quant questions faster and better - Join in and bookmark this topic or subscribe to it to get notifications when new topics and tips get posted.

Number Properties:
PS question
DS Question
Tips and hints

Divisibility/Multiples/Factors:
PS question
DS question
Tips and hints

Remainders:
PS question
DS question
Tips and hints

Inequalities:
PS question
DS question
Tips and hints

Absolute Values:
PS question
DS question
Tips and hints

Algebra:
PS question
DS question
Tips and hints

Exponents and roots:
PS question
DS question
Tips and hints

Combinations:
PS question
DS question

Every week we'll be publishing 2 brand new (PS an DS) questions from each and every topic tested on the GMAT along with respective tips and hints.
Get Kudos points for correct solutions.
Share your tips and hints below and get Kudos points

Attachment:

hints-tricks-shortcuts.jpg [ 4.87 KiB | Viewed 46933 times ]

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Originally posted by Bunuel on 03 Jun 2014, 06:01.
Last edited by Bunuel on 26 Jul 2014, 16:13, edited 37 times in total.
MBA Section Director
Affiliations: GMAT Club
Joined: 22 Feb 2012
Posts: 7111
City: Pune
Re: Tips and Hints for Specific Quant Topics (with Examples)  [#permalink]

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26 Jul 2014, 11:23
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Here is a Tip on work/rate problems. I would like to introduce Percent approach to solve Work/rate problems.

Let's consider basic example.
A can complete a certain task in 10 hours and B can complete the same task 20 hours.
We assume that the task is 100%
So if A can complete the task in 10 hours, we can say he is taking 10 hours to complete 100% of task. That means in one hour he is finishing $$\frac{100%}{10}$$ or 10% task.
Similarly B is completing $$\frac{100%}{20}$$ or 5% task in one hour.
If they start working together(at their respective rates), they would finish (10% + 5%) or 15% task in one hour.
So to finish entire task together, it would take them $$\frac{100}{15}$$ or $$6\frac{2}{3}$$ hours.

Now lets apply this logic on following GMAT Type question. This is question is taken from Bunuel's Set of Mixed questions.

Three workers, A, B, and C, can complete a certain task in 10, 5 and x hours respectively. A starts working alone and 2 hours later B joins. After another 2 hours joins C. After that A, B, and C together complete the task in 15 minutes. What is the value of x?

A. 1
B. 1.25
C. 2
D. 2.5
E. 4

Three workers, A, B, and C, can complete a certain task in 10, 5 and x hours respectively
So in one hour A is completing 10% task, B is completing 20% task, and C is completing $$(\frac{100}{x})%$$ task.

A starts working alone and 2 hours later B joins.
Before B joins, A will have worked for 2 hours and have finished 20% task. That means when B joins A, total remaining work will be 80%

After another 2 hours joins C.
Using Similar logic, At the time of C's joining, A & B will have finished 60% task. Remaining work will be 20%

After that A, B, and C together complete the task in 15 minutes.
So A, B, C together complete remaining 20% task in 15 mins or in $$\frac{15}{60} hours$$

So we have that $$\frac{20%}{(10% + 20% + 100/x)} = \frac{15}{60}$$

Solving for X, we get 750x = 1500 ----------> x = 2

Hope that helps!!
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##### General Discussion
Math Expert
Joined: 02 Sep 2009
Posts: 58402
Re: Tips and Hints for Specific Quant Topics (with Examples)  [#permalink]

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26 Jul 2014, 16:13
_________________
Math Expert
Joined: 02 Sep 2009
Posts: 58402
Re: Tips and Hints for Specific Quant Topics (with Examples)  [#permalink]

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04 Jan 2018, 03:52
Bump..................................
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Re: Tips and Hints for Specific Quant Topics (with Examples)   [#permalink] 04 Jan 2018, 03:52
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