Last Updated on May 3, 2023
GMAT OFFICIAL GUIDE PS
Solution:
Although this problem may seem wordy and confusing, it has much more bark than bite. In the given equation, we have variables L, d, and S, and the entire equation is set equal to N.
We also are told the following:
N = the number of cars in a certain instant in time
L = number of lanes in the same direction
d = length of the portion of the highway, in feet
s = average speed of the cars, in miles per hour
We are given the following values for the variables:
d = ½ mile
L = 2 lanes
s = 40 mph
Before plugging these values into the equation, we must convert ½ mile to feet. Since we know that (5,280 feet = 1 mile), we know that:
½ mile = ½ x 5,280 = 2,640 feet
So now we can plug all this info into the equation to determine the estimated number of cars N.
N = (20Ld)/(600 + s^2)
N = (20 x 2 x 2,640)/(600 + 40^2)
N = (40 x 2,640)/2,200
N = (4 x 264)/22
N = (2 x 264)/11
N = 528/11 = 48
Answer: D
Note: Notice that at the end we kept reducing our equation so that we did not have to work with numbers that were too large; keep things as simple as possible.
