Bunuel wrote:

Members of a wrestling team were weighed twice. Was the standard deviation of their weights at the second weighing greater than the standard deviation of their weights at the first weighing?

(1) The second weighing showed that, since the first weighing, half of the team had lost 1 pound, while the other half had gained 1 pound.

(2) The standard deviation of all the weights at the first weighing was 0 pounds.

Questions involving standard deviations often rely on basic properties of the standard deviation and not calculations.

We'll look for such a solution, a Logical approach.

(1) Since the standard deviation reflects 'how far apart the datapoints are from each other', or, in equations, is calculated based on the differences of all values from the mean, then this statement is exactly what we need! If half the team lost 1 pound and the other gained 1 pound, the mean stayed the same but all the weights were further apart from it (so the std increased).

Sufficient.

(2) Since this gives us no information on the second weighing, it can't be enough. (Trivia: the standard deviation is 0 only when all of the numbers are equal!)

Insufficient.

(A) is our answer.

_________________

Sign up for 7-day free trial