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Donna has a 60 miles drive to a work conference...

by AAPL » Fri Feb 09, 2018 12:42 pm
Donna has a 60 miles drive to a work conference. She begins driving at 30 miles per hour, but halfway through the drive, she realizes she is going to be late and speed up. How fast should she drive the remaining distance (in miles per hour) if she needs to complete the entire trip in 90 minutes?

A. 55
B. 60
C. 65
D. 70
E. 88

The OA is B.

We know that the total distance is 60 miles and the total time that she needs to complete the entire trip is 90 minutes or 1.5 hours.

She drove the first 30 miles in an hour because she begins driving at 30 miles per hour, that's mean that the remaining distance is 30 miles.

Then, she will drive the last 30 miles at a rate of, speed = 30 miles / 0.5 hours = 60 miles per hour to complete the trip in 90 minutes.

Is there another strategic approach to solve this PS question? Can any experts help, please? Thanks.
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by EconomistGMATTutor » Sun Feb 11, 2018 3:18 am
AAPL wrote:Donna has a 60 miles drive to a work conference. She begins driving at 30 miles per hour, but halfway through the drive, she realizes she is going to be late and speed up. How fast should she drive the remaining distance (in miles per hour) if she needs to complete the entire trip in 90 minutes?

A. 55
B. 60
C. 65
D. 70
E. 88

The OA is B.

We know that the total distance is 60 miles and the total time that she needs to complete the entire trip is 90 minutes or 1.5 hours.

She drove the first 30 miles in an hour because she begins driving at 30 miles per hour, that's mean that the remaining distance is 30 miles.

Then, she will drive the last 30 miles at a rate of, speed = 30 miles / 0.5 hours = 60 miles per hour to complete the trip in 90 minutes.

Is there another strategic approach to solve this PS question? Can any experts help, please? Thanks.
Hi AAPL.

Let's take a look.

We know she has to drive 60 miles in 90 minutes. Now, we are asked for miles per HOUR. Hence, let's make the conversion from minutes to hours.

Therefore, 90 minutes = 90/60 = 1.5 hours.

Now, Donna drove halfway at 30 miles per hour, this implies that she drove 60/2 = 30 miles at 30 miles per hour. That is to say, that she has driven for ONE hour.

Now, if she wants to arrive on time, she has to drive 30 miles in 1.5 - 1 = 0.5 hours. This implies that she has to drive at $$30\ miles\ =\ V\cdot0.5\ hours\ \Leftrightarrow\ V=60\ miles\ per\ hour.$$ So, the correct answer is the option B.

I hope this answer can help you.

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

Regards.
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by Scott@TargetTestPrep » Wed Feb 14, 2018 10:21 am
AAPL wrote:Donna has a 60 miles drive to a work conference. She begins driving at 30 miles per hour, but halfway through the drive, she realizes she is going to be late and speed up. How fast should she drive the remaining distance (in miles per hour) if she needs to complete the entire trip in 90 minutes?

A. 55
B. 60
C. 65
D. 70
E. 88
The first 30 miles take 30/30 = 1 hour.

She needs to complete the next 30 miles in 3/2 - 1 = 1/2 hour.

So she must drive at a rate of 30/(1/2) = 60 miles per hour.

Answer: B

Scott Woodbury-Stewart
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[email protected]

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