1.  A particular model of an airconditioner cost $ 700 five years ago. The same model costs $ 945 today. By what percent has the cost increased? 

Hint
Halfnhalf Clue
 

2.  A gas cylinder has two vents, V1 and V2, for discharge. The cylinder empties in 7 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.  A large water reservoir has two outlet pipes, a small one and a large one. It takes 7 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? 
 Halfnhalf Clue
 

4.  Of the S students enrolled in a Programming Course, 90% take the Certification Examination. 50% of the students who take the Certification Examination pass it. In this Certification Examination, students who pass the examination are what percent of the students enrolled in the Programming Course? 
 Halfnhalf Clue
 
