"At a primate reserve, the mean age of all the male primates is 15 years, and the mean age of all female primates is 19 years!" demands the Proctor, pointing an accusing finger at Xena. "Which of the following must be true about the mean age m of the combined group of male and female primates at the primate reserve?"

There is a moment of dumbfounded silence.

"Who cares?" Xena says, staring incredulously at the Proctor.