A certain number of answer sheets can be checked in 12 days working 5 hours each day by 9 examiners. For how many hours a day should 4 examiners work to check twice the number of answer sheets in 30 days ?
A. 4 hours
B. 8 hours
C. 7 hours
D. 9 hours
Answer : D. 9 hours
Explanation:
Let required number of hours be x
More examiners, less hours(indirect proportion)
More days, less hours(indirect proportion)
More answer books, more hours(direct proportion)
Hence we can write as
-
- 9 * 12 * 2 * 5 = 4 * 30 * 1 * x
-
- x = 9 * 12 * 2 * 5 / 4 * 30 * 1
-
- = 9 * 3 * 2 * 5 / 30
- = 9
