Question

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.

Answer 1

Let the speed of the car be "X". From 3 am until 1 pm (10 hours), the car will travel 10*X 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: 

10*X = 2*(x+200)= 2x+400 
Subtract 2*X from both sides: 
8*X = 400
X = 400/8 = 50 mph. 

Hope this helps.