It is currently 12 Dec 2018, 14:27
My Tests

Close

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

GRE Quantitative Comparison Tip #5 – Estimation with a Twist

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
1 KUDOS received
Director
Director
User avatar
Joined: 16 May 2014
Posts: 594
GRE 1: Q165 V161
Followers: 92

Kudos [?]: 439 [1] , given: 64

GRE Quantitative Comparison Tip #5 – Estimation with a Twist [#permalink] New post 03 Aug 2014, 10:54
1
This post received
KUDOS
Expert's post

Strategy#5 Estimation with a Twist


In the last post we discussed the following question
Attachment:
q1.png
q1.png [ 9.63 KiB | Viewed 1478 times ]

Our approach was to first recognize that two of fractions are approximately 1/2 and two are approximately 1/3.

Now if we had used these approximations, we would have been left with:
Attachment:
q2.png
q2.png [ 2.13 KiB | Viewed 1478 times ]

This would have made us conclude (incorrectly) that the answer is C.

To solve this question using approximation, we applied a twist. We recognized that 213/428 is a little bit less than 1/2, which we denoted as 1/2-. We also noticed that 3007/9101 is a little bit less than 1/3, which we denoted as 1/3-.

And so on.

With these little twists, we were able to simplify the two columns as:
Attachment:
q3.png
q3.png [ 2.21 KiB | Viewed 1476 times ]

From here, it was clear that the correct answer is B

Okay, now let’s see if you can apply this approximation with a twist to solve the following question:
Attachment:
q4.png
q4.png [ 3.52 KiB | Viewed 1476 times ]

Aside: before you read my solutions, see if you can find additional ways to solve this question.

Okay, first we’ll solve the question using approximation with a twist, and then we’ll solve it using different approaches.

Approximation with a twist:


First, let’s approximate as follows:
Attachment:
q5.png
q5.png [ 3.05 KiB | Viewed 1478 times ]

From here, we can drop 4 zeroes from each number to get:
Attachment:
q6.png
q6.png [ 2.86 KiB | Viewed 1476 times ]

At this point, I’ll apply a nice rule that says: \(A*B=2A*{1/2}B\)

In other words, the product of two numbers is equal to the product of twice one number and half the other value.

So, in Column A, we’ll double 45+ and halve 64+ to get:
Attachment:
q7.png
q7.png [ 2.56 KiB | Viewed 1475 times ]

From here, when we compare the products in parts, we can see that Column A must be greater than Column B, so the answer is A.

Alternative approach #1



As you might have guessed, the two original products are too large to work on a calculator. For example, (641,713)x(451,222)=289,555,023,286 and this number is too large for the GRE’s onscreen calculator. As such, the calculator would display an error message if you tried to perform this calculation.

There are, however, some ways to work around this constraint and still use the calculator.

For example, you could divide each number by 1000 to get:
Attachment:
q8.png
q8.png [ 3.12 KiB | Viewed 1477 times ]

point, the products will still fit into the display of the onscreen calculator and you would clearly see that Column A is greater.



Alternative approach #2



Another possible approach is to perform the same steps we performed earlier, but stop when we get to:
Attachment:
q9.png
q9.png [ 2.8 KiB | Viewed 1477 times ]

Originally, we applied that handy rule where we double one number and halve the other. However, we could also use the calculator at this point.

(64)x(45)=2880 and (90)x(32)=2880. This means that (64+)x(45+)=2880+ and (90-)x(32-)=2880-.

So, we get:
Attachment:
q10.png
q10.png [ 2.14 KiB | Viewed 1475 times ]

Once again we see the answer is A.
_________________

My GRE Resources
Free GRE resources | GRE Prep Club Quant Tests
If you find this post helpful, please press the kudos button to let me know ! :)

Intern
Intern
Joined: 18 Feb 2017
Posts: 8
Followers: 0

Kudos [?]: 2 [0], given: 0

Re: GRE Quantitative Comparison Tip #5 – Estimation with a Twist [#permalink] New post 16 Mar 2017, 02:23
What stops me from solving this on the calculator? Pretty sure this can be solved with it in under 2 mins?
GMAT Club Legend
GMAT Club Legend
User avatar
Joined: 07 Jun 2014
Posts: 4749
GRE 1: Q167 V156
WE: Business Development (Energy and Utilities)
Followers: 93

Kudos [?]: 1657 [0], given: 396

CAT Tests
Re: GRE Quantitative Comparison Tip #5 – Estimation with a Twist [#permalink] New post 16 Mar 2017, 04:14
Expert's post
annyo wrote:
What stops me from solving this on the calculator? Pretty sure this can be solved with it in under 2 mins?


Calculator is a viable option.
_________________

Sandy
If you found this post useful, please let me know by pressing the Kudos Button

Try our free Online GRE Test

GRE Instructor
User avatar
Joined: 10 Apr 2015
Posts: 1234
Followers: 46

Kudos [?]: 1116 [0], given: 7

Re: GRE Quantitative Comparison Tip #5 – Estimation with a Twist [#permalink] New post 25 Mar 2017, 07:18
Expert's post
Here's a video that expounds on Sandy's post:

_________________

Brent Hanneson – Creator of greenlighttestprep.com
Image
Sign up for our free GRE Question of the Day emails

GRE Instructor
User avatar
Joined: 10 Apr 2015
Posts: 1234
Followers: 46

Kudos [?]: 1116 [0], given: 7

Re: GRE Quantitative Comparison Tip #5 – Estimation with a Twist [#permalink] New post 25 Mar 2017, 07:21
Expert's post
annyo wrote:
What stops me from solving this on the calculator? Pretty sure this can be solved with it in under 2 mins?

You can always use the onscreen calculator.
HOWEVER, that calculator is VERY CLUNKY, and its functionality may not be the same as calculators you're familiar with.
Also keep in mind that, if you can use some quick (3 second) estimation and solve a question in less time, then you can use that extra time for other questions.

RELATED VIDEO FROM OUR COURSE

_________________

Brent Hanneson – Creator of greenlighttestprep.com
Image
Sign up for our free GRE Question of the Day emails

Re: GRE Quantitative Comparison Tip #5 – Estimation with a Twist   [#permalink] 25 Mar 2017, 07:21
Display posts from previous: Sort by

GRE Quantitative Comparison Tip #5 – Estimation with a Twist

  Question banks Downloads My Bookmarks Reviews Important topics  


cron

GRE Prep Club Forum Home| About| Terms and Conditions and Privacy Policy| GRE Prep Club Rules| Contact

Powered by phpBB © phpBB Group

Kindly note that the GRE® test is a registered trademark of the Educational Testing Service®, and this site has neither been reviewed nor endorsed by ETS®.