Best approach for VIC problems

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melguy: Master | Next Rank: 500 Posts; Posts: 335; Joined: Mon Mar 21, 2011 11:31 pmFollowed by: 2 members; Location: Australia / India; Thanked: 37 times

by melguy » Mon Nov 21, 2016 3:49 am

Hello All

I would like to seek some advice on VIC problems. I am curious if its worth learning a new approach for these kind of problem or selecting values for variables x,y and z etc and testing 5 options is the best approach (even though a bit time consuming).

Also, is it safe to assume that one should not see more than 1 or 2 VIC questions on the real exam so there should be sufficient time to select values and test answers manually for a question like below

If x percent of y is equal to y percent less than z, what is y in terms of x and z?

1. 100 (x+z)
--------------
x

2. 100x
--------
x+z

3. 100 (x+z)
--------
x-z

4. 100z
-------
x-z

5. 100z
---------
x+z

Thanks

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Source: Beat The GMAT — Problem Solving | Mon Nov 21, 2016 3:49 am

GMATGuruNY: GMAT Instructor; Posts: 15539; Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members; Location: New York, NY; Thanked: 13060 times; GMAT Score:790

by GMATGuruNY » Mon Nov 21, 2016 4:40 am

melguy wrote:Hello All

I would like to seek some advice on VIC problems. I am curious if its worth learning a new approach for these kind of problem or selecting values for variables x,y and z etc and testing 5 options is the best approach (even though a bit time consuming).

Also, is it safe to assume that one should not see more than 1 or 2 VIC questions on the real exam so there should be sufficient time to select values and test answers manually for a question like below

If x percent of y is equal to y percent less than z, what is y in terms of x and z?

1. 100 (x+z)
--------------
x

2. 100x
--------
x+z

3. 100 (x+z)
--------
x-z

4. 100z
-------
x-z

5. 100z
---------
x+z

Thanks

Plugging in numbers can be very efficient here.

y percent less than z.
Let z=1 and y=100, with the result that y percent less than z is 100 percent less than 1 -- a nice result, since 100 percent less than 1 = 0.

x percent of y is equal to y percent less than z.
Since y=100 and y percent less than z = 0, we get:
x percent of 100 is equal to 0.
Thus, x=0.

The question stem asks for the value of y = 100.
Now plug x=0 and z=1 into the answers to see which yields our target of 100.

Since A will yield a denominator of 0, eliminate A.
Since B will yield a numerator of 0, eliminate B.
Since C and D will each yield a denominator that is negative, eliminate C and D.

The correct answer is E.

Please note that there is no "best" approach.
For some test-takers, algebra will be the most efficient way to solve this problem.
For other test-takers, plugging in numbers will be the most efficient way.
The trick is to determine the best way for YOU.

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My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

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GMATGuruNY: GMAT Instructor; Posts: 15539; Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members; Location: New York, NY; Thanked: 13060 times; GMAT Score:790

by GMATGuruNY » Mon Nov 21, 2016 4:53 am

melguy wrote:f x percent of y is equal to y percent less than z, what is y in terms of x and z?

1. 100 (x+z)
--------------
x

2. 100x
--------
x+z

3. 100 (x+z)
--------
x-z

4. 100z
-------
x-z

5. 100z
---------
x+z

Algebra:

x percent of y is equal to y percent less than z.
(x/100)(y) = z - (y/100)z
xy = 100z - yz
xy + yz = 100z
y(x+z) = 100z
y = (100z)/(x+z).

The correct answer is E.

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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 » Mon Nov 21, 2016 7:08 am

melguy wrote:Hello All

I would like to seek some advice on VIC problems. I am curious if its worth learning a new approach for these kind of problem or selecting values for variables x,y and z etc and testing 5 options is the best approach (even though a bit time consuming).

You're right; selecting and testing values (aka the INPUT-OUTPUT approach) can be time-consuming. Also, there's the chance that, on your first pass, you may only eliminate 2 or 3 answer choices, in which case you need to test a new set of values with the remaining answer choices. Many students prefer the Input-Output approach, because it involves little or no algebra, but the ALGEBRAIC approach is often much faster.

If you'd like more information on these approaches, we have some videos:
- Variables in the Answer Choices - https://www.gmatprepnow.com/module/gmat- ... /video/933
- Tips for the Algebraic Approach - https://www.gmatprepnow.com/module/gmat- ... /video/934
- Tips for the Input-Output Approach - https://www.gmatprepnow.com/module/gmat- ... /video/935

Also, I recently wrote two articles about solving VIC questions:
https://www.gmatprepnow.com/articles/var ... approaches
https://www.gmatprepnow.com/articles/var ... 93-part-ii

Finally, here are some more questions to practice with:
- https://www.beatthegmat.com/what-mistake ... 76293.html
- https://www.beatthegmat.com/car-dealer-s ... 74136.html
- https://www.beatthegmat.com/ps-rate-times-t276107.html
- https://www.beatthegmat.com/to-find-the- ... 73338.html
- https://www.beatthegmat.com/y-dollars-fr ... 73031.html
- https://www.beatthegmat.com/meters-in-x- ... 73854.html
- https://www.beatthegmat.com/a-better-exp ... 79396.html

Brent Hanneson - Creator of GMATPrepNow.com

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DavidG@VeritasPrep: Legendary Member; Posts: 2663; Joined: Wed Jan 14, 2015 8:25 amFollowed by: 128 members; Location: Boston, MA; Thanked: 1153 times; GMAT Score:770

by DavidG@VeritasPrep » Mon Nov 21, 2016 8:10 am

melguy wrote:Hello All

I would like to seek some advice on VIC problems. I am curious if its worth learning a new approach for these kind of problem or selecting values for variables x,y and z etc and testing 5 options is the best approach (even though a bit time consuming).

Also, is it safe to assume that one should not see more than 1 or 2 VIC questions on the real exam so there should be sufficient time to select values and test answers manually for a question like below

If x percent of y is equal to y percent less than z, what is y in terms of x and z?

1. 100 (x+z)
--------------
x

2. 100x
--------
x+z

3. 100 (x+z)
--------
x-z

4. 100z
-------
x-z

5. 100z
---------
x+z

Thanks

You'll notice also that in many of these questions, the correct answer will end up being D or E. It kind of makes sense - if most test-takers start with A, it's a more time-consuming question if the correct answer is D or E. So on these types of questions, I'll often encourage students to start with E and work their way up. (Just know that this won't work 100% of the time.)

Some more examples for practice:

https://www.beatthegmat.com/stocks-price ... 87975.html

https://www.beatthegmat.com/last-sunday- ... 58328.html

Veritas Prep | GMAT Instructor

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