Bob wants to run a mile in the same time as his sister.

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Vincen: Legendary Member; Posts: 2898; Joined: Thu Sep 07, 2017 2:49 pm; Thanked: 6 times; Followed by:5 members

Bob wants to run a mile in the same time as his sister.

by Vincen » Wed Jan 03, 2018 12:08 pm

Bob wants to run a mile in the same time as his sister. If Bob's time for a mile is currently 10 minutes 40 seconds and his sister's time is currently 9 minutes 36 seconds, by what percent does Bob need to improve his time in order run a mile in the same time as his sister?

(A) 3%
(B) 5%
(C) 8%
(D) 10%
(E) 12%

The OA is the option D.

What is the equation that I should use here to solve this PS question? I need some help experts. I ask for your help.

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Source: Beat The GMAT — Problem Solving | Wed Jan 03, 2018 12:08 pm

EconomistGMATTutor: GMAT Instructor; Posts: 555; Joined: Wed Oct 04, 2017 4:18 pm; Thanked: 180 times; Followed by:12 members

by EconomistGMATTutor » Wed Jan 03, 2018 1:10 pm

Hello Vincen.

Let's take a look at your question.

First of all, let's convert the time to seconds.

Bob's time = 640 secs.
His sister's time = 576 secs.

Now, if we improve the time of Bob by 10% we can get that the new time is: 640 - 64 = 576 secs.

So, the correct answer is the option [spoiler]D=10%[/spoiler].

I hope this explanation may help you.

I'm available if you'd like a follow-up.

Regards.

GMAT Prep From The Economist
We offer 70+ point score improvement money back guarantee.
Our average student improves 98 points.

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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 Aug 12, 2019 5:45 pm

Vincen wrote:Bob wants to run a mile in the same time as his sister. If Bob's time for a mile is currently 10 minutes 40 seconds and his sister's time is currently 9 minutes 36 seconds, by what percent does Bob need to improve his time in order run a mile in the same time as his sister?

(A) 3%
(B) 5%
(C) 8%
(D) 10%
(E) 12%

The OA is the option D.

What is the equation that I should use here to solve this PS question? I need some help experts. I ask for your help.

We should notice that in this question, "improving the time" means decreasing the time; therefore, we are looking for a percent decrease.

Bob's time is 10 40/60 = 10 2/3 = 32/3 minutes

His sister's time is 9 36/60 = 9 6/10 = 9 3/5 = 48/5 minutes

If we let n = the percent less, we have:

(32/3) x (100 - n)/100 = 48/5

(100 - n)/100 = 48/5 x 3/32

(100 - n)/100 = 3/5 x 3/2

(100 - n)/100 = 9/10

100 - n = 90

n = 10%

Alternate Solution:

Bob's current time is 10 minutes 40 seconds = 640 seconds.

His sister's current time is 9 minutes 36 seconds = 576 seconds.

Bob must improve his time by 640 - 576 = 64 seconds, and that is an improvement of (64/640) * 100 = 10 percent.

Answer: D

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