1.  A large water reservoir has two outlet pipes, a small one and a large one. It takes 9 hours to empty the reservoir when only the small outlet pipe is open. It takes 2 hours to empty the reservoir when only the large outlet pipe is open. About what fraction of the reservoir will be emptied in one hour if both the pipes are open? 

Hint
Halfnhalf Clue
 

2.  A gas cylinder has two vents, V1 and V2, for discharge. The cylinder empties in 6 minutes when only vent V1 is open. The cylinder empties in 3 minutes when both vent V1 and vent V2 are open. About how many minutes will the cylinder take to empty if only vent V2 is open? 
 Halfnhalf Clue
 

3.  Mr. Kennedy bought 600 shares of ABC Inc. in 1997 at a price of $ 8 for each share. He sold all these shares yesterday for 60% more than he paid for them. If he has to pay a tax of 20% on the gain, how many dollars does he pay as tax? 
 Halfnhalf Clue
 

4.  There are 720 animals on a farm. Threefourths of them are cows. Of the cows, about 50% are white. How many cows on the farm are not white? 
 Halfnhalf Clue
 
