By what percent is 25 greater than 15?

Jay@ManhattanReview: GMAT Instructor; Posts: 3008; Joined: Mon Aug 22, 2016 6:19 am; Location: Grand Central / New York; Thanked: 470 times; Followed by:34 members

by Jay@ManhattanReview » Thu Jan 10, 2019 10:18 pm

BTGmoderatorDC wrote:By what percent is 25 greater than 15?

(A) 10%
(B) 25%
(C) 33 1/3%
(D) 60%
(E) 66 2/3%

OA E

Source: Manhattan Prep

25 is greater than 15 by 10 (= 25 - 15). Thus, 25 is greater than 15 by (10/15)*100% = 66 2/3%.

The correct answer: E

Hope this helps!

-Jay
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shashank.ism: Legendary Member; Posts: 1022; Joined: Mon Jul 20, 2009 11:49 pm; Location: Gandhinagar; Thanked: 41 times; Followed by:2 members

by shashank.ism » Fri Jan 11, 2019 1:09 am

BTGmoderatorDC wrote:By what percent is 25 greater than 15?

(A) 10%
(B) 25%
(C) 33 1/3%
(D) 60%
(E) 66 2/3%

OA E

Source: Manhattan Prep

25/15 = 5/3 = 1.6666
So, 25 is greater than 15 by .666666 x100 %
= 66.66%

Answer E

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fskilnik@GMATH: GMAT Instructor; Posts: 1449; Joined: Sat Oct 09, 2010 2:16 pm; Thanked: 59 times; Followed by:33 members

by fskilnik@GMATH » Fri Jan 11, 2019 6:03 am

BTGmoderatorDC wrote:By what percent is 25 greater than 15?

(A) 10%
(B) 25%
(C) 33 1/3%
(D) 60%
(E) 66 2/3%
Source: Manhattan Prep

$$15\,\,\mathop \to \limits^{?\,\, = \,\,\Delta \% } \,\,25$$
$$? = {{25 - 15} \over {15}} = {2 \over 3}\,\,\,\,\, \Rightarrow \,\,\,\,\left( {\rm{E}} \right)$$

This solution follows the notations and rationale taught in the GMATH method.

Regards,
Fabio.

Fabio Skilnik :: GMATH method creator ( Math for the GMAT)
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GMAT/MBA Expert

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

by Brent@GMATPrepNow » Fri Jan 11, 2019 7:06 am

BTGmoderatorDC wrote:By what percent is 25 greater than 15?

(A) 10%
(B) 25%
(C) 33 1/3%
(D) 60%
(E) 66 2/3%

An alternative approach is to test the answer choices

First, however, we can eliminate some answer choices by first testing an easy value: 50%

Is 25 50% greater than 15?
Well, 50% of 15 = 7.5
So, 50% greater than 15 = 15 + 7.5 = 22.5
22.5 is too small (we need to get 25), so we need a percentage that's greater than 50%
So, we can ELIMINATE A, B and C

Now we'll test answer choice D: 60%
Is 25 60% greater than 15?
60% of 15 = 9
So, 60% greater than 15 = 15 + 9 = 24 (no good - we need 25)
We can ELIMINATE D

By the process of elimination, the correct answer is E

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

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Scott@TargetTestPrep: GMAT Instructor; Posts: 8086; Joined: Sat Apr 25, 2015 10:56 am; Location: Los Angeles, CA; Thanked: 43 times; Followed by:29 members

by Scott@TargetTestPrep » Mon Jan 21, 2019 5:35 pm

BTGmoderatorDC wrote:By what percent is 25 greater than 15?

(A) 10%
(B) 25%
(C) 33 1/3%
(D) 60%
(E) 66 2/3%

We can create the following expression:

(25 - 15)/15 x 100 = 10/15 x 100 = 2/3 x 100 = 66 â…”%

Alternate Solution:

We see that 25 is 10 more than 15. Thus, 25 is 10/15 greater than 15. We see that 10/15 = 2/3 â‰ˆ 0.67, or 67%

Answer: E

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