SOLUTION: A plane travels 100 mph in still air. It travels 240 miles into the wind and 240 miles with the wind in a total time of 5 hours. Find the wind speed.

Algebra ->  Customizable Word Problem Solvers  -> Travel -> SOLUTION: A plane travels 100 mph in still air. It travels 240 miles into the wind and 240 miles with the wind in a total time of 5 hours. Find the wind speed.      Log On

Ad: Over 600 Algebra Word Problems at edhelper.com


   



Question 723156: A plane travels 100 mph in still air. It travels 240 miles into the wind and
240 miles with the wind in a total time of 5 hours. Find the wind speed.

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +w+ = the wind speed in mi/hr
+100+%2B+w+ = the plane's speed going with the wind in mi/hr
+100+-+w+ = the plane's speed going against the wind in mi/hr
Let +t+ = plane's time going against the wind in hrs
+5+-+t+ = planes time going with the wind in hrs
----------------
Equation going against the wind:
(1) +240+=+%28+100+-+w+%29%2At+
Equation going with the wind:
(2) +240+=+%28+100+%2B+w+%29%2A%28+5+-+t+%29+
-----------------------------
(2) +240+=+500+%2B+5w+-+100t+-+w%2At+
(2) +w%2At+%2B+100t+-+5w+=+260+
(2) +t%2A%28+100+%2B+w+%29+=+260+%2B+5w+
and,
(1) +240+=+%28+100+-+w+%29%2At+
(1) +t+=+240+%2F+%28+100+-+w+%29+
Substitute this result into (2)
(2) ++%28240+%2F+%28+100+-+w+%29%29+%2A%28+100+%2B+w+%29+=+260+%2B+5w+
(2) +240%2A%28+100+%2B+w+%29+=+%28+260+%2B+5w+%29%2A%28+100+-+w+%29+
(2) +24000+%2B+240w+=+26000+%2B+500w+-+260w+-+5w%5E2+
(2) +5w%5E2+=+2000+
(2) +w%5E2+=+400+
(2) +w+=+20+
The wind speed is 20 mi/hr
------------------------
check answer:
(1) +240+=+%28+100+-+w+%29%2At+
(1) +240+=+%28+100+-+20+%29%2At+
(1) +240+=+80t+
(1) +t+=+3+ hrs
and
(2) +240+=+%28+100+%2B+w+%29%2A%28+5+-+t+%29+
(2) +240+=+%28+100+%2B+20+%29%2A%28+5+-+t+%29+
(2) +240+%2F+120+=+5+-+t+
(2) +2+=+5+-+t+
(2) +t+=+3+ hrs
OK