<PRE><B>Question 370897</B>
An airliner leaves Phoenix traveling at an average rate of 420 mph.
 Thirty minutes later, a second airliner leaves Phoenix traveling along a parallel route.
 If the second plane overtakes the first at a point 1680 miles from Phoenix, find its rate.
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Convert 30 min to .5 hrs
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Let r = speed of the 2nd plane
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Write a time equation, time = dist/speed
:
1st plane time = 2nd plane time + .5 hrs
{{{1680/420}}} = {{{1680/r}}} + .5
 4 - .5 = 1680/r
3.5r = 1680
r = 1680/3.5
r = 480 mph 
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You can check this solution by finding the actual travel time of each</PRE>