Need help with easy distance problem

Test Preparation SAT Preparation
1

<p>I know this is easy but I cant get the right answer.........</p>

<p>Breanna drove 720 miles to visit some friends. She averaged 60 miles per hour on
the trip out. Coming back, she wanted her drive to be two hours shorter. How
many miles per hour faster must she drive on the way back to do this?</p>

2

<p>Is answer 12 miles per hour?</p>

3

<p>yes, I am obviously reading it incorrectly…how did you do it?</p>

4

<p>Average velocity=total distance/total time</p>

<p>60=720/x
x=12 hours</p>

<p>60+x=720/10
60+x=72
x=12 miles per hour</p>

5

<p>But honestly, this question is from ACT Math preparation. So it should be posted in ACT thread.
[ACT</a> Preparation - College Confidential](<a href=“http://talk.collegeconfidential.com/act-preparation/]ACT”>ACT Preparation - College Confidential Forums)</p>

6

<p>Basic formula is distance = rate * time.</p>

<p>For the trip from A to B, you know distance and rate, so solve for time: t = d/r = 720 miles/60 miles per hour = 12 hours.</p>

<p>For the trip from B to A, you know distance and time (“two hours shorter” => t = 12 - 2 = 10 hours), so solve for rate: r = d/t = 720 miles/10 hours = 72 miles per hour.</p>

<p>Now the questions reads “how many miles per hour <em>faster</em> …” Take the rate from B to A and subtract the rate from A to B: r = 72 - 60 = 12 miles per hour faster.</p>

7

<p>^
Didn’t I write the same solution?</p>

8

<p>Yours wasn’t there when I started mine. No big deal.</p>