Two boats are heading towards each other at constant speeds of 3 miles/hr and 21 miles/hr respectively. They begin at a distance 20 miles from each other. How far are they (in miles) one minute before they collide ? Select.
A) 1/12	B) 5/12	C) 1/6	D) 1/3	E) 3/15
The question asks: how far apart will they be 1 minute=1/60 hours before they collide?   Since the combined rate of the boats is  3+21= 
<gadget id="calculator"> 3+21</gadget>
<output>24</output>
24 mph then 1/60 hours before they collide they'll be rate*time=distance --&gt; 24*1/60=3/15 miles apart.   Answer: 3/15.
<result>E</result>
Two boats are heading towards each other at constant speeds of 3 miles/hr and 21 miles/hr respectively. They begin at a distance 20 miles from each other. How far are they (in miles) one minute before they collide ?