A data set has coefficient of variation 20 percent and variance 144. Find its mean.

The standard deviation is √144 = 12. From CV = (standard deviation ÷ mean) × 100 we get 20 = (12 ÷ mean) × 100, so the mean is 1200 ÷ 20 = 60. Putting the variance 144 into the formula in place of the standard deviation would wrongly give 720.