A contractor agrees to build a bridge in 300 days. He employs 10 workers. After 150 days, he finds that only half the work is complete. How many additional workers does he need to finish on time?
A5 workers
B10 workers
C15 workers
D20 workers
Correct Answer:
B. 10 workers
Explanation:
Remaining days = 150. Remaining work = 1/2. Current productivity = (1/2 work)/(150 days × 10 workers) = 1/3000 per worker-day. Required rate = (1/2)/(150 × x) where x is total workers. x = 10. So need 10 additional workers.
A and B together can complete a work in 12 days. A alone can complete it in 20 days. In how many days can B alone complete the work?
A25 days
B30 days
C35 days
D40 days
Correct Answer:
B. 30 days
Explanation:
Work done by A in 1 day = 1/20. Work done by A+B in 1 day = 1/12. So B's work in 1 day = 1/12 - 1/20 = (5-3)/60 = 2/60 = 1/30. Therefore B takes 30 days.
A pipe can fill a tank in 15 hours. Another pipe can empty it in 20 hours. If both pipes are opened together, in how many hours will the tank be filled?
A45 hours
B50 hours
C60 hours
D75 hours
Correct Answer:
C. 60 hours
Explanation:
Filling rate = 1/15 per hour. Emptying rate = 1/20 per hour. Net rate = 1/15 - 1/20 = (4-3)/60 = 1/60. Time = 60 hours.
If a number is increased by 25%, and then decreased by 20%, what is the net change?
A5% increase
B2% decrease
C1% increase
DNo change
Correct Answer:
A. 5% increase
Explanation:
Let original number = 100. After 25% increase = 125. After 20% decrease of 125 = 125 × 0.8 = 100. Wait, let me recalculate: 125 × (100-20)/100 = 125 × 80/100 = 100. Net change = 0. Actually answer is D (No change). Let me verify: 1.25 × 0.8 = 1. So net is no change. Correction: The answer should be D.
Two workers A and B are paid ₹500 and ₹600 per day respectively. If A completes a job in 24 days and B completes it in 18 days, who is more cost-effective?
AA is more cost-effective
BB is more cost-effective
CBoth are equally cost-effective
DCannot be determined
Correct Answer:
B. B is more cost-effective
Explanation:
Total cost for A = 500 × 24 = ₹12,000. Total cost for B = 600 × 18 = ₹10,800. B costs less, so B is more cost-effective.
