A survey of some AP* Stats students recorded gender and whether the student was left or right-handed. Results were summarized in a table like the one shown. If it turned out that handedness was independent of gender, how many of the AP* Stats students were lefty girls? $\begin{array}{|c|c|c|c|}
\hline& \text { Lefty } & \text { Righty } & \text { Total } \
\hline \text { Boy } & & & 66 \
\hline \text { Girl } & ? & & 54 \
\hline \text { Total } & 20 & 100 & 120 \
\hline
\end{array}$
A) 4
B) 9
C) It cannot be determined.
D) 10
E) 7

Question

Quizplus · Accepted Answer

If handedness is independent of gender, the proportion of lefties should be the same across boys and girls. There are 20 lefties out of 120 students, so the proportion of lefties is $20/120 = 1/6$. For girls, $1/6$ of 54 is 9, so there would be 9 lefty girls.

A Survey of Some AP* Stats Students Recorded Gender and Whether