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How Fast Did Dan Drive?

Date: 8/24/96 at 19:28:24
From: Anonymous
Subject: How fast did Dan drive?

I need an equation for this problem:

It takes Kay 20 minutes to drive to work at 45 mph. Two minutes after 
she left home this morning, her husband Dan started out with her 
briefcase, which she had forgotten. If Dan gets to the office just as 
Kay does, how fast did he drive?

Thanks,  Dustin

Date: 8/25/96 at 15:15:32
From: Doctor Robert
Subject: Re: How fast did Dan drive?

Be careful not to mix minutes with miles per HOUR.  Kay drives at 
45 mph for 1/3 of an hour, so she drives 45 x 1/3 = 15 miles.  
Now Dan drives the same distance in 18 minutes (since he left two 
minutes after she did).  Therefore, his speed must be distance 
divided by time:

   v = 15/(18/60hr) = 50 mph

-Doctor Robert,  The Math Forum
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