答案
总共有50个人做题,40个人做对A题,31个人做对B题,有4个人两道题目都做错了。问:有多少人是两道题都做对的? QkP5Rb5HL0mD4sDudKm2EPDJhphi1aveHZDerQ8ZvzGURKURiIGOtAwfHt1WME1l