Hi All,

We're told that Oscar is running in a straight line away from Nancy at the rate of 20 feet per second, Nancy is chasing Oscar at the rate of 25 feet per second and Oscar has a 100-foot head start. We're asked for the number of seconds it will it take Nancy to catch Oscar. This is an example of a 'chase down' question and can be solved in a couple of different ways (all of which use some variation on the Distance Formula).

Since Nancy is running 25 feet per second and Oscar is running 20 feet per second, once they are BOTH running, Nancy will 'catch up' by 25 - 20 = 5 feet per second. Oscar has a 'head start' of 100 feet, so we can use the Distance Formula to calculate how long it will take Nancy to catch Oscar:

Dist. = (Rate)(Time)
100 ft. = (5 ft/sec)(T)
100/5 = T
20 secs = T

Final Answer: D

GMAT assassins aren't born, they're made,
Rich

BTGmoderatorLU wrote:Source: Princeton Review

Oscar is running in a straight line away from Nancy at the rate of 20 feet per second. Nancy is chasing Oscar at the rate of 25 feet per second. If Oscar has a 100-foot head start, how long, in seconds, will it take Nancy to catch Oscar?

A. 4
B. 5
C. 10
D. 20
E. 100

Since the difference in rates is 25 - 20 = 5 ft/sec, which means that for each second, Nancy reduces the distance between them by 5 feet. Thus, the number of seconds it takes for Nancy to catch Oscar is 100/5 = 20.

Answer: D