On a physical fitness test middle school boys are awarded one point for each push-up they can do, and a point for each sit-up. National results showed that boys average 18 pushups with a standard deviation of 4 push-ups, and 34 sit-ups with standard deviation 11. The mean of their combined (total) scores was therefore 18 + 34 = 52 points. What is the standard deviation of their combined scores?
A) It cannot be determined.
B) 137
C) 15
D) 11.7
E) 5.3

Question

Quizplus · Accepted Answer

The standard deviation of the combined scores cannot be determined from the given information because the correlation between the push-ups and sit-ups is not provided. The standard deviation of a sum of variables depends on both their individual standard deviations and the correlation between them.

On a Physical Fitness Test Middle School Boys Are Awarded