Question 169681
We know from the givens that 2/3 of the students are under grads and 1/3 are grads.
:
now 1/4 of the under grads commute{{{(1/4)(2/3)=2/12=1/6}}} which is the amount of undergrads that commute--->
of that 1/10 drive more than 40 miles{{{(1/10)(1/6)=1/60}}}undergrads drive more than 40 miles.
:
now 1/3 of the grads commute{{{(1/3)(1/3)=1/9}}}which is the amount of grads that commute----->
of that 1/6 drive more than 40 miles{{{(1/6)(1/9)=1/54}}}grads that drive more than 40 miles.
:
now we only need add  the amount of under grads and grads that commute more than 40 miles.....
{{{(1/60)=(1/54)=19/540=.035}}} so 3.5% of commuters drive more than 40 miles