A can complete a work in 10 days. B can complete the same work in 15 days. If they work together for 3 days and then A leaves, how many more days will B take to finish?
A5 days
B6 days
C7 days
D8 days
Correct Answer:
B. 6 days
Explanation:
Work rate A = 1/10, B = 1/15. Combined = 5/30 = 1/6. In 3 days = 3/6 = 1/2 work done. Remaining = 1/2. B's time = (1/2)/(1/15) = 7.5 days
Two trains of lengths 150m and 250m are moving towards each other at speeds of 45 km/h and 35 km/h. How long will they take to completely pass each other?
A18 seconds
B20 seconds
C24 seconds
D30 seconds
Correct Answer:
A. 18 seconds
Explanation:
Total length = 400m. Relative speed = 45 + 35 = 80 km/h = 80 × 5/18 = 22.22 m/s. Time = 400/22.22 ≈ 18 seconds
A tank can be filled by pipe A in 20 hours and by pipe B in 30 hours. Both pipes are opened for 10 hours, then pipe A is closed. How long will pipe B take to fill the remaining tank?
A5 hours
B7.5 hours
C10 hours
D12 hours
Correct Answer:
A. 5 hours
Explanation:
Rate A = 1/20, Rate B = 1/30. Combined = 5/60. In 10 hours = 50/60. Remaining = 10/60. B's time = (10/60)/(1/30) = 5 hours
