Question 965150


An airplane takes 3.6 hours to fly 1800 miles against the wind. It only takes the plane 3 hours to return 1800 miles with the wind. Assuming that the plane flies at a constant speed, how long will it take it to fly 3300 miles when there is no wind?
<pre>Let speed in calm air be S, and wind, W
To travel 1,800 miles in 3.6 hours against the wind, total speed = {{{1800/3.6}}}, or 500 mph
We then have: S - W = 500 ------- eq (i)

To travel 1,800 miles in 3 hours with the wind, total speed = {{{1800/3}}}, or 600 mph
We then have: S + W = 600 ------- eq (ii)
2S = 1,100 ------- Adding eqs (ii) & (i)
S, or speed in still air = {{{1100/2}}}, or 550 mph

Time taken to travel 3,300 miles in calm air = {{{3300/550}}}, or {{{highlight_green(6)}}} hours