GMAT PROBLEM SOLVING FRACTIONS

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rbansal: Senior | Next Rank: 100 Posts; Posts: 36; Joined: Tue Jul 20, 2010 7:42 pmFollowed by: 1 member; Thanked: 1 times

by rbansal » Wed Apr 13, 2011 3:01 pm

Can Someone please post the fastest way to get to the solution:

Q: 43

The Sum 7/8 + 1/9 is between?

a)1/2 and 3/4
b)3/4 and 1
c)1 and 1 1/4
d)1 1/4 and 1 1/2
e)1 1/2 and 2

Thank you,

RB

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Source: Beat The GMAT — Problem Solving | Wed Apr 13, 2011 3:01 pm

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Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members; Location: Vancouver, BC; Thanked: 5254 times; GMAT Score:770

by Brent@GMATPrepNow » Wed Apr 13, 2011 3:07 pm

rbansal wrote:Can Someone please post the fastest way to get to the solution:

Q: 43

The Sum 7/8 + 1/9 is between?

a)1/2 and 3/4
b)3/4 and 1
c)1 and 1 1/4
d)1 1/4 and 1 1/2
e)1 1/2 and 2

Thank you,

RB

Well, first we know that 7/8 + 1/8 = 1
Since 1/9 is a little bit less than 1/8, we know that the sum 7/8 + 1/9 will be a little bit less than 1.
Since 7/8 is also greater than 3/4, the answer must be B

Last edited by Brent@GMATPrepNow on Sun May 01, 2016 10:03 am, edited 1 time in total.

Brent Hanneson - Creator of GMATPrepNow.com

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JVeld: Newbie | Next Rank: 10 Posts; Posts: 4; Joined: Sat Feb 19, 2011 2:32 pm

by JVeld » Fri Apr 15, 2011 5:49 am

I solved this problem by simply adding the fractions together. I got 71/72, and the only answer that makes sense is B, since 71/72 is slightly less than 1.

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SarahLiz: Junior | Next Rank: 30 Posts; Posts: 10; Joined: Thu Mar 24, 2011 6:46 am; Location: Schaumburg, IL; Thanked: 2 times

by SarahLiz » Fri Apr 15, 2011 5:58 am

I also added the fractions (this doesn't take long at all) to get 71/72, which is just less than 1. So, B.

Test date: 5/18/2011

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vikrambansal: Senior | Next Rank: 100 Posts; Posts: 38; Joined: Thu Mar 19, 2015 2:32 amFollowed by: 1 member; Location: India; GMAT Score:550

by vikrambansal » Fri May 15, 2015 4:48 am

Even I found adding much simple.

Brent - I'm reviewing wrong questions as per 60 day study guide. What do you say?

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Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members; Location: Vancouver, BC; Thanked: 5254 times; GMAT Score:770

by Brent@GMATPrepNow » Fri May 15, 2015 7:45 am

vikrambansal wrote:Even I found adding much simple.

Brent - I'm reviewing wrong questions as per 60 day study guide. What do you say?

Both solutions are fast and easy.
It really comes down to number sense. If you feel confident in your number sense, then my earlier approach is fine. Otherwise, stick with making the calculations.

Here's an another example of what I mean:

Let's say you're working on a GMAT question that requires you to find a certain percent. After some work, you get to the point where you must convert 11/49 into an approximate percent. What do you do from here?
Well, as always, we should check the answer choices before performing any calculations. If the answer choices are sufficiently spread apart, we can use some alternative techniques based on estimation and number sense.

Let's say that the 5 answer choices are as follows:

(A) 19.8%
(B) 21.6%
(C) 22.4%
(D) 39.4%
(E) 40.6%

Here's a fast approach that involves number sense:
We know that 11/50 = 22%
So, 11/49 will be a bit BIGGER than 22%.
So, C must be the correct answer. Done!

If you feel confident in your number sense, then this kind of approach is quite fast.
If you don't feel confident, then you might need to perform a bit of long division and divide 11 by 49.
Once again, both approaches work.

Conclusion: play to your strengths

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

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[email protected]: Elite Legendary Member; Posts: 10392; Joined: Sun Jun 23, 2013 6:38 pmFollowed by: 511 members; Location: Palo Alto, CA; Thanked: 2867 times; GMAT Score:800

by [email protected] » Fri May 15, 2015 9:10 am

Hi vikrambansal,

Many Test Takers face pacing problems while dealing with either the Quant or Verbal section (or both). Pacing problems don't exist on their own though - they're the results of OTHER problems.

In this question, there are 2 reasonably "quick" ways to get to the correct answer, but which way is really faster for YOU. Considering those two methods, how much faster is the "faster" option?

Let's say it's 10 seconds faster.....

Now, imagine if "your way" of answering a question is always 10 seconds SLOWER than the faster option....

37 questions x 10 seconds slower =
370 seconds =
6 minutes 10 seconds

So, you might inadvertently be wasting LOTS of time and not even realize it because you're getting the question correct. This is all meant to say that you should be reviewing the questions that you get CORRECT as well as the ones that you get incorrect....and practicing multiple approaches. In that way, you should be able to develop a sense of which method is faster for any given situation (and at the very least, you'll be less likely to get "stuck" on a question if the first approach that you try doesn't seem to 'work').

GMAT assassins aren't born, they're made,
Rich

Contact Rich at [email protected]

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