请问ＮＮ们两道PREP的数学题。快考试了， 急啊！

1。 According to the diections on a can of frozon orange juice on a can of forzon organge juice concentrate, 1 can of concentrate is to be mixed with 3 cans of water ro make orange. How many 12-ounce cans of the concentrate are required to prepare 200 6-ounce orange juice . ( 答案是：２５）

2。pumps A, B,C & D operate at their respective constant rates. pumps A ＆Ｂ，operating simultaneously, can fill the tank in 6/5 hour; pumps A &Ｃ,operting simuateously,can fill the tank in 3/2 hours; pumps B&C, work simuateously, can fill the tank in 2 hours. How many hours does it take pumps A,B &C  work simuateously to fill the tank. ( 答案是：1 hour)
        

题目可能很简单，请ＮＮ们不要笑！ 多谢了！

1 can of concentrate is to be mixed with 3 cans of water ro make orange

所以1/4是concentrate

200 6-ounce orange juice 

共1200ounce,乘以1/4是300,所以共需300的concentrate

300/12=25

我是先算3个情况的效率,A和B一起工作的效率是5/6,A和C是2/3,B和C是1/2,

所以2个A 2个B 2个C一起工作一小时可以完成5/6+2/3+1/2=12/6=2

所以ABC一起的话,需要1小时.