Problem Solving

Hi Vincen,

We're told that Barbara walked up and down a 25 meter long corridor. When she walked one way, she walked at 4 meters per second, and when she walked the other way, her speed was 2 meters per second. We're asked for her average speed in meters per second for the entire trip. This question is a standard "Average Speed" question and can be solved with a bit of math.

Walking the 25 meters at 4 meters/second:
Distance = (Rate)(Time)
25m = (4m/sec)(T)
25/4 seconds = Time

Walking the 25 meters at 2 meters/second:
Distance = (Rate)(Time)
25m = (2m/sec)(T)
25/2 = 12.5 seconds = Time

Total Distance = 25m + 25m = 50 meters
Total Time = 25/4 + 25/2 = 25/4 + 50/4 = 75/4 seconds

Total Distance = (Av. Speed)(Total Time)
50m = (Av. Speed)(75/4 seconds)
(50)(4/75) = Av. Speed
200/75 =
8/3 =
2 1/3 meters/second = Average Speed

Final Answer: D

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

Vincen wrote:Barbara walked up and down a 25 meter long corridor. When she walked one way, she walked at 4 meters per second, and when she walked the other way, her speed was 2 meters per second. What was her average speed in meters per second?

$$A.\ \ \ 1\frac{1}{3} $$
$$B.\ \ \ 1\frac{2}{3}\ \ .$$
$$C.\ \ \ 2\frac{1}{3}\ \ .$$
$$D.\ \ \ 2\frac{2}{3}\ \ .$$
$$E.\ \ \ 3$$

We can use the average rate formula:

average rate = total distance/total time

average = 50/(25/4 + 25/2)

average = 50/(25/4 + 50/4)

average = 50/(75/4)

average = 200/75 = 8/3 = 2 2/3

Answer: D