关于GMAT数学题的问题

关于GMAT数学题的问题
on a certain transatlantic crossing,20 percent of a ship's passengers held round-trip tickets and also took their cars abroad the ship.if 60 percent of the passengers with round-trip tickets did not take their cars abroad the ship,what percent of the ship's passengers held round-trip tickets?
在一次横渡大西洋中,20%的乘客有round-trip然后带着他们的车上船.如果60%的乘客有round-trip没有带车上船,问：有多少百分比的乘客有round-trip?
a.33.3333333%b.40%c.50%d.60% e.66.6666666666666%
机经上的一道题~~~做不来
Freiheit1218提到：持有往返票（round-trip）并带着车的占总乘客数的20%；所有持有往返票的乘客中，没带车的占60%。
那么也就是说：持有往返票并带着车的乘客占总乘客数的（1-60%）
也就是说题目其实在问实际乘船人数和理论乘船人数的百分比是伐！？