Question 166202
<pre>
a plane which can fly 520mph in still air flies for 3 hours against a wind and for 2 hours with the same wind.
The total distance it covers is 2565 miles. find rate of the wind.
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Speed, in still air: 520 mph

Let wind-speed be W
Average speed, against the wind: 520 - W
Average speed, with the wind: 520 + W 

Distance travelled against the wind, in 3 hours: 3(520 - W) = 1,560 - 3W
Distance travelled with the wind, in 2 hours: 2(520 + W) = 1,040 + 2W

With the TOTAL DISTANCE travelled being 2,565 miles, we get the following TOTAL DISTANCE equation:
1,560 - 3W + 1,040 + 2W = 2,565 
      - 3W + 2,600 + 2W = 2,565
              - 3W + 2W = 2,565 - 2,600
                    - W = - 35
   Speed of wind, or {{{matrix(1,5, W, "=", (- 35)/(- 1), "=", highlight(matrix(1,2, 35, mph)))}}}</pre>