求教一道数学题~~为什么还不换题库哎

alexnerohero

On a recent trip, Mary drove 50 miles.What was the average speed at which she drove the 50 miles?

(1)She drove 30 miles at an average speed of 60 miles per hour and then drove the remaining 20 miles at an average speed of 50 miles per hour.

(2)She drove a total of 54 minutes.

（1）能不能满足呢？？？ drove the remaining 20 miles at an average speed of 50 miles per hour.这段时间未知啊？？？？怎么算AVERAGE呢

论坛设施

时间位置，您把20/50 不就是时间了吗……
崩溃