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Confused with Distance, rate and time formula

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Confused with Distance, rate and time formula

by Sak32 » Wed Nov 06, 2013 11:14 am
The typical distance formula is: Rate x time = Distance

Yet this problem uses the formula with: Distance x Rate = Time

I need to know why please. Its very confusing.

After driving to a riverfront parking lot, Bob plans to run south along the river, turn around, and return to the parking lot, running north along the same path. After running 3.25 miles south, he decides to run for only 50 minutes more. If Bob runs at a constant rate of 8 minutes per mile, how many miles farther south can he run and still be able to return to the parking lot?

The answer is 1.5 miles.
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by ganeshrkamath » Wed Nov 06, 2013 11:19 am
Sak32 wrote:The typical distance formula is: Rate x time = Distance

Yet this problem uses the formula with: Distance x Rate = Time

I need to know why please. Its very confusing.

After driving to a riverfront parking lot, Bob plans to run south along the river, turn around, and return to the parking lot, running north along the same path. After running 3.25 miles south, he decides to run for only 50 minutes more. If Bob runs at a constant rate of 8 minutes per mile, how many miles farther south can he run and still be able to return to the parking lot?

The answer is 1.5 miles.
Total distance to be covered in 50 minutes = 3.25 + 2d
Speed = 1 mile/8 minutes = 1/8 miles/minute

Distance = speed * time
3.25 + 2d = (1/8) * (50)
2d = 6.25 - 3.25
2d = 3
d = 1.5 miles

NOTE: Speed is given as 8 minutes/mile, which is the reason for rate * distance = time

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by [email protected] » Wed Nov 06, 2013 11:50 am
Hi Sak32,

ganeshrkamath has properly explained the math behind this question, so I won't rehash that here.

While the GMAT will throw a variety of "standard" formulas/concepts at you, the adaptive nature of the Test means that as you show a consistent ability to answer questions correctly, the program will throw you "non-standard" versions of questions. Sometimes these questions will test your knowledge or rarer formulas or your ability to spot hidden patterns. In this case, the "twist" involves taking a non-standard rate (8 minutes per mile) and converting it into speed (60/8 = 15/2 = 7.5 miles/hour) so that you can answer the question. Pay very careful attention to the information that a prompt gives you; converting information into other formats is a necessary skill to score at a high level in the Quant section.

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Rich
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