An airplane travels 1800 miles in 3 hours flying with the wind. On the return trip, flying against the wind, it takes 4 hours to travel 20000 miles. Find the rate of the wind and the rate of the plane in still air.

Andrew and Michael are 15 miles apart. If they walk towards each other, they meet in 3
hours. If they both walk in the same direction, Michael overtakes, Andrew in 8 hours.
How fast does each boy walk?

75 miles miles an hour. (First one)

5 mph for the second one.

Step by Step:

1800%2F3 = u + v   (1)  is the equation for the flight with the wind.

                     (Here "u" is the airspeed of the airplane with NO wind,

                           "v" is the wind speed)

1800%2F4 = u - v   (2)  is the equation for the flight against the wind.

Simplify equations (1) and (2) and write them as a system:

u + v = 600,           (1')

u - v = 450.           (2')

Now add the two equations (1') and (2'). You will get

2u = 1050  --->  u = 1050%2F2 = 525 miles per hour.

Having this, you can easily determine "v" from (1'):  

v = 600 - 525 = 75 miles per hour.

Second one will be 15 divided by 3 = 5mph

the first one, all those points on the line just make a strait line.