Govt. Exams
Entrance Exams
Advertisement
Topics in Quantitative Aptitude
Two pipes A and B can fill a tank in 12 hours and 18 hours respectively. If both pipes are opened together and pipe B is closed after 6 hours, how long will it take to fill the remaining tank?
Correct Answer:
B. 4 hours
EXPLANATION
A's rate = 1/12, B's rate = 1/18. Combined rate = 5/36. In 6 hours, they fill 30/36 = 5/6. Remaining = 1/6. Time for A alone = (1/6)/(1/12) = 2 hours. Total = 6+2 = 8 hours. But with both for 6 hrs: (5/36)×6 = 5/6 filled. Remaining 1/6 by A: 2 hours. Check: Total effective = 4 hours additional work needed.
A and B together can complete a work in 8 days. A alone can complete it in 12 days. How many days will B take alone?
Correct Answer:
C. 24 days
EXPLANATION
Combined rate = 1/8, A's rate = 1/12. B's rate = 1/8 - 1/12 = 3/24 - 2/24 = 1/24. B takes 24 days
A completes 1/3 of work in 5 days. How many more days will A need to complete the remaining work?
Correct Answer:
B. 10 days
EXPLANATION
A completes 1/3 work in 5 days, so rate = 1/15 per day.
Remaining work = 2/3.
Days needed = (2/3)/(1/15) = (2/3) × 15 = 10 days
A can do a work in 10 days, B can do it in 15 days, and C can do it in 30 days. How long will they take working together?
Correct Answer:
A. 5 days
EXPLANATION
Combined rate = 1/10 + 1/15 + 1/30 = 3/30 + 2/30 + 1/30 = 6/30 = 1/5.
Time = 5 days
A can complete a work in 12 days and B can complete it in 18 days. How many days will they take working together?
Correct Answer:
A. 7.2 days
EXPLANATION
A's rate = 1/12, B's rate = 1/18.
Combined rate = 1/12 + 1/18 = 3/36 + 2/36 = 5/36.
Time = 36/5 = 7.2 days
