Two cars are traveling in the same direction along the same route. The

Question

Two cars are traveling in the same direction along the same route. The red car travels at a constant speed of 40 miles per hour, and the black car is traveling at a constant speed of 50 miles per hour. If the red car is 20 miles ahead of the black car, how many hours will it take the black car to overtake the red car?

A. 0.1
B. 0.6
C. 1
D. 1.2
E. 2

Nidzo · Answer

Relative speed: 50 - 40 = 10

Time = Distance/Speed
20/10 = 2 hours

Answer E

GMATWhizTeam · Answer

Solution:

As of now, the gap between the cars: 20 miles.

After 1 hour: 
Red car travel 40 miles and Black car travel 50 miles. 
the distance between the cars reduces to 10 miles in 1 hour.

So the rate of gap reduction = 10 miles/hour

so to end the full gap of 20 miles, it would take =  \frac{20}{10} = 2   hours.

Alternative Solution:

There is a direct formula to get this answer. 
The time in which both these cars will come together =  \frac{distance between them }{ difference of their speeds}=\frac{20}{10}=2  hours.

Hence the right answer is Option E.

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