RATIO OF TWO QUANTITIES

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oquiella: Master | Next Rank: 500 Posts; Posts: 164; Joined: Tue May 12, 2015 9:06 am; Thanked: 3 times

by oquiella » Mon Oct 05, 2015 4:31 pm

THE RATIO OF TWO QUANTITIES IS 3 TO 4. IF EACH OF THE QUANTITIES IS INCREASED BY 5, WHAT IS THE RATIO OF THESE TWO NEW QUANTITIES?

A. 3/4
B. 8/9
C. 18/19
D. 23/24
E. IT CANNOT BE DETERMINED FROM THE INFORMATION GIVEN

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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 Oct 05, 2015 4:37 pm

oquiella wrote:THE RATIO OF TWO QUANTITIES IS 3 TO 4. IF EACH OF THE QUANTITIES IS INCREASED BY 5, WHAT IS THE RATIO OF THESE TWO NEW QUANTITIES?

A. 3/4
B. 8/9
C. 18/19
D. 23/24
E. IT CANNOT BE DETERMINED FROM THE INFORMATION GIVEN

Test two cases and see what happens.

case 1: x = 3 and y = 4, so the ratio x/y = 3/4
Now add 5 to both quantities to get:
x = 8 and y = 9, so the NEW ratio = 8/9

case 2: x = 6 and y = 8, so the ratio x/y = 6/8 = 3/4
Now add 5 to both quantities to get:
x = 11 and y = 13, so the NEW ratio = 11/13

Answer: E

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] » Mon Oct 05, 2015 5:03 pm

Hi oquiella,

When dealing with a starting ratio, it's important to remember that the ratio does NOT actually tell you how many "items" you're dealing with. Here, we're given a starting ratio of 3 to 4, but we don't know the exact number of each item - we just know how they relate to one another (for every 3 we have of the first, we have 4 of the second).

Thus, the actual values are limitless...
3 and 4
6 and 8
9 and 12
12 and 16
Etc.

As Brent showed in his explanation, adding 5 to both values does NOT yield a consistent result, so the ending ratio cannot be determined (which is to say that it can have more than one possible value).

Final Answer: E

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

Contact Rich at [email protected]

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Max@Math Revolution: Elite Legendary Member; Posts: 3991; Joined: Fri Jul 24, 2015 2:28 amFollowed by: 37 members; Location: Las Vegas, USA; Thanked: 19 times

by Max@Math Revolution » Tue Oct 06, 2015 9:06 pm

Forget conventional ways of solving math questions. In PS, IVY approach is the easiest and quickest way to find the answer.

THE RATIO OF TWO QUANTITIES IS 3 TO 4. IF EACH OF THE QUANTITIES IS INCREASED BY 5, WHAT IS THE RATIO OF THESE TWO NEW QUANTITIES?

A. 3/4
B. 8/9
C. 18/19
D. 23/24
E. IT CANNOT BE DETERMINED FROM THE INFORMATION GIVEN

Let the two quantities be a and b. Then we have a/b= 3/4, that means 4a=3b. We can put a=3k and b=4k. We should find the ratio (a+5)/(b+5)=(3k+5)/(4k+5). That means, however, (3k+5)/(4k+5) has different value depending on the value of k. So we cannot determine the ratio of (a+5) to (b+5) with only information above. The answer is, therefore, E)

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Scott@TargetTestPrep: GMAT Instructor; Posts: 8137; Joined: Sat Apr 25, 2015 10:56 amFollowed by: 29 members; Location: Los Angeles, CA; Thanked: 43 times

by Scott@TargetTestPrep » Tue Dec 12, 2017 11:29 am

oquiella wrote:The ratio of two quantities is 3 to 4. If each of the quantities is increased by 5, what is the ratio of these two new quantities?

A. 3/4
B. 8/9
C. 18/19
D. 23/24
E. It cannot be determined from the information given.

We are given that the ratio of two quantities is 3 to 4 or 3x to 4x. When each quantity is increased by 5, we have:

(3x + 5)/(4x + 5)

We see that this is not enough information to determine a new ratio.

For instance, if x = 1, then (3x + 5)/(4x + 5) = 8/9; however, if x = 2, then (3x + 5)/(4x + 5) = 11/13.

Since 8/9 does not equal 11/13, we cannot determine a unique value of the new ratio.

Answer: E

Scott Woodbury-Stewart
Founder and CEO
[email protected]

See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews

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