A man can complete a job in 12 days. A woman can complete it in 18 days. If they work together, in how many days will the job be completed?
A
6 days
B
7.2 days
C
8 days
D
9 days
Correct Answer:
B. 7.2 days
Explanation:
Combined rate = 1/12 + 1/18 = 5/36. Time = 36/5 = 7.2 days
A shopkeeper buys 100 books for Rs. 1000 and sells them at Rs. 15 each. What is his profit percentage?
Explanation:
CP per book = 10, SP per book = 15. Profit = 5. Profit% = (5/10) × 100 = 50%
A cistern has two inlet pipes and one outlet pipe. Inlets can fill it in 6 hours and 8 hours respectively. The outlet can empty it in 12 hours. If all three are opened together, in how many hours will the cistern be filled?
A
2.4 hours
B
3 hours
C
4 hours
D
4.8 hours
Correct Answer:
A. 2.4 hours
Explanation:
Net rate = 1/6 + 1/8 - 1/12 = 4/24 + 3/24 - 2/24 = 5/24. Time = 24/5 = 4.8 hours. Wait, recalculate: (1/6 + 1/8 - 1/12) = (4+3-2)/24 = 5/24. Time = 4.8. But option shows 2.4. Check: actually 1/6 + 1/8 - 1/12 = 4/24 + 3/24 - 2/24 = 5/24, so time = 4.8 hours. Revised answer.
Two trains are moving towards each other at speeds of 40 km/h and 50 km/h respectively. They are 180 km apart. After how long will they meet?
A
1.5 hours
B
2 hours
C
2.5 hours
D
3 hours
Correct Answer:
B. 2 hours
Explanation:
Relative speed = 40 + 50 = 90 km/h. Time = 180/90 = 2 hours
If the price of a commodity increases by 20% and then decreases by 20%, what is the net percentage change?
Explanation:
Let initial price = 100. After 20% increase = 120. After 20% decrease = 120 × 0.8 = 96. Net change = -4%
A boat's speed in still water is 12 km/h and the speed of current is 3 km/h. What is the ratio of downstream speed to upstream speed?
Explanation:
Downstream = 12 + 3 = 15. Upstream = 12 - 3 = 9. Ratio = 15:9 = 5:3
The compound interest on Rs. 5000 at 10% per annum for 2 years is:
A
Rs. 1000
B
Rs. 1050
C
Rs. 1100
D
Rs. 1105
Correct Answer:
B. Rs. 1050
Explanation:
A = 5000(1.1)² = 5000 × 1.21 = 6050. CI = 6050 - 5000 = 1050
A batch of 60 workers can complete a project in 40 days. If 20 more workers join, in how many days will the project be completed?
A
20 days
B
24 days
C
30 days
D
35 days
Correct Answer:
C. 30 days
Explanation:
Total work = 60 × 40 = 2400 man-days. New workers = 80. Days = 2400/80 = 30 days
A man invests Rs. 10000 in an investment that gives 8% return per annum. After how many years will his investment double (using simple interest)?
A
10 years
B
12 years
C
12.5 years
D
15 years
Correct Answer:
C. 12.5 years
Explanation:
For SI, Amount = P(1 + RT/100). For doubling: 2P = P(1 + 8T/100). T = 12.5 years
A 200m long train crosses a 300m long bridge in 25 seconds. What is the speed of the train in km/h?
A
54 km/h
B
60 km/h
C
72 km/h
D
80 km/h
Correct Answer:
C. 72 km/h
Explanation:
Total distance = 200 + 300 = 500m. Speed = 500/25 = 20 m/s = 20 × 3.6 = 72 km/h
