Speed and distance problems are one type of question you will have to answer on the GMAT math section. They will appear in both problem solving and data sufficiency questions. The key equation for speed and distance problems is:
However, usually problems will not be as simple as, “The speed is 20 miles per hour and the time is five hours, what is the distance?” In most GMAT math problems, you will have to manipulate the equation to find the solution.
Take a look at this sample GMAT math question:
Bus A leaves LA at 6 p.m. and heads directly to San Francisco. Bus A goes 60 miles an hour and does not make any stops. Bus B leaves San Francisco two hours later, and heads directly to LA. Bus B also does not make any stops. LA and San Francisco are 390 miles apart. The buses pass each other at 10 p.m. How fast is Bus B going?
- 70 mph.
- 75 mph.
- 80 mph.
- 95 mph.
- 100 mph.
Since the buses are approaching each other from Los Angeles and San Francisco respectively, when they cross each other their distances will add up to the distance between the two cities (390 miles).
The distance that Bus A traveled when they pass each other can be figured out by multiplying its speed (60 mph) by the total time it traveled (four hours). We know it is four hours, because it leaves at 6 p.m. and they cross at 10 p.m. Thus it travels:
(60mph)(4 hours)=240 miles
That means that Bus B has traveled 150 miles over a period of two hours, because it left two hours after Bus A. That means it is traveling at a speed of:
150 miles/2 hours=75mph (B)
Similar to other question types in GMAT math, speed and distance problems need to be broken down into their simplest form. Then, the basic equations can be manipulated in order to figure out the correct answer.
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