SOLUTION: A plane, that can fly an average of 400 mph in still air, makes frequent round trips from city A to city B. When the wind is blowing at an average rate of 20 mph the flying time fo

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Question 1080258: A plane, that can fly an average of 400 mph in still air, makes frequent round trips from city A to city B. When the wind is blowing at an average rate of 20 mph the flying time for the entire round trip is 12 hours. how far is it from city A to city B?
Found 2 solutions by josmiceli, MathTherapy:
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
The plane's speed flying with the wind is:
+400+%2B+20+=+420+ mi/hr
The plane's speed flying against the wind is:
+400+-+20+=+380+ mi/hr
Let +d+ = the distance between A and B
Let +t+ = time in hrs flying with the wind
+12+-+t+ = time in hrs flying against the wind
----------------------------------------------
Flying with the wind:
(1) +d+=+420t+
Flying against the wind:
(2) +d+=+380%2A%28+12+-+t+%29+
-------------------------
Plug (1) into (2)
(2) +420t+=+380%2A%28+12+-+t+%29+
(2) +420t+=+4560+-+380t+
(2) +800t+=+4560+
(2) +t+=+5.7+
---------------------------
(1) +d+=+420t+
(1) +d+=+420%2A5.7+
(1) +d+=+2394+
The distance from A to B is 2,394 mi
------------------------------------
check:
(2) +d+=+380%2A%28+12+-+t+%29+
(2) +d+=+380%2A%28+12+-+5.7+%29+
(2) +d+=+380%2A6.3+
(2) +d+=+2394+
OK

Answer by MathTherapy(10549) About Me  (Show Source):
You can put this solution on YOUR website!

A plane, that can fly an average of 400 mph in still air, makes frequent round trips from city A to city B. When the wind is blowing at an average rate of 20 mph the flying time for the entire round trip is 12 hours. how far is it from city A to city B?
Let distance from A to B, be D
Time traveled AGAINST wind: matrix%281%2C3%2C+D%2F%28400+-+20%29%2C+or%2C+D%2F380%29
Time traveled WITH wind: matrix%281%2C3%2C+D%2F%28400+%2B+20%29%2C+or%2C+D%2F420%29
We then get the following TIME equation: D%2F380+%2B+D%2F420+=+12
21D + 19D = 95,760 ------- Multiplying by LCD, 7,980
40D = 95,760
D, or distance from A to B =