The average speed of one airplane is 200 mph faster than that of an automobile. If the automobile starts at 3 a.m. and the airplane starts from the same place at 11 a.m., they will have traveled the same number of miles by 1:00 p.m. Find the rate of the automobile.
Let the speed of the car be "X". From 3 am until 1 pm (10 hours), the car will travel 10X miles.
The speed of the aeroplane is (X +200). From 11 am until 1 pm (2 hours), the plane will travel 2(X+200).
The distance travelled is the same, so:
10X = 2(x+200)= 2x+400
Subtract 2X from both sides:
8X = 400
X = 400/8 = 50 mph.
Hope this helps.