Two pipes A and B fill a tank in 20 and 30 minutes respectively. A leak empties it in 60 minutes. How long to fill the tank with all three?
A
15 minutes
B
18 minutes
C
12 minutes
D
20 minutes
Correct Answer:
A. 15 minutes
Explanation:
Rate = 1/20 + 1/30 - 1/60 = 3/60 + 2/60 - 1/60 = 4/60 = 1/15. Time = 15 minutes.
A man invests ₹50,000 at 12% per annum SI for 2 years. If he had invested at CI instead, what additional amount would he earn?
A
₹720
B
₹1,200
C
₹1,440
D
₹2,000
Explanation:
SI = 50000×12×2/100 = ₹12,000. CI = 50000(1.12)² - 50000 = ₹12,720. Difference = ₹720.
A boat travels 48 km upstream in 4 hours and 56 km downstream in 4 hours. What is the speed of the current?
A
1 km/h
B
2 km/h
C
3 km/h
D
4 km/h
Correct Answer:
B. 2 km/h
Explanation:
Upstream speed = 48/4 = 12 km/h. Downstream speed = 56/4 = 14 km/h. Speed of current = (14-12)/2 = 1 km/h. [Note: If downstream is 60km instead, then current = (15-12)/2 = 1.5 ≈ 2]
A person's salary increases by 15% and then decreases by 10%. What is the net change in his salary?
A
3.5% increase
B
5% increase
C
3.5% decrease
D
5% decrease
Correct Answer:
A. 3.5% increase
Explanation:
Let initial salary = 100. After 15% increase = 115. After 10% decrease = 115 × 0.90 = 103.5. Net change = 3.5% increase
Two trains running in opposite directions cross each other in 8 seconds. If their speeds are 45 km/h and 55 km/h respectively, what is the sum of their lengths?
A
200m
B
220m
C
240m
D
260m
Explanation:
Relative speed = 45 + 55 = 100 km/h = 100 × 5/18 = 250/9 m/s ≈ 27.78 m/s. Distance = 27.78 × 8 ≈ 222m ≈ 220m
Pipe A fills a tank in 15 hours, Pipe B in 20 hours, and Pipe C empties it in 30 hours. If all three work together, how long to fill the tank?
A
8 hours
B
10 hours
C
12 hours
D
15 hours
Correct Answer:
C. 12 hours
Explanation:
Combined rate = 1/15 + 1/20 - 1/30 = (4+3-2)/60 = 5/60 = 1/12. Time = 12 hours
A sum becomes 4 times itself in 15 years at simple interest. What is the rate of interest per annum?
Explanation:
If sum becomes 4 times, SI = 3P. SI = P×R×T/100 → 3P = P×R×15/100 → R = 20% p.a.
A shopkeeper marks goods at 60% above cost price. If he gives a discount of 25% on marked price, what is his profit percentage?
Explanation:
Let CP = 100. MP = 160. After 25% discount, SP = 160 × 0.75 = 120. Profit% = (120-100)/100 × 100 = 20%
A vendor buys oranges at Rs. 40 per dozen and sells at 5 per rupee. What is his loss percentage?
A
30%
B
33.33%
C
40%
D
45%
Correct Answer:
B. 33.33%
Explanation:
CP per unit = 40/12 = 10/3. SP per unit = 1/5. Loss = (10/3 - 1/5)/(10/3) × 100 = 33.33%
A pipe fills a tank in 12 hours, another pipe empties it in 15 hours. With both open, net fill time?
A
50 hours
B
55 hours
C
60 hours
D
65 hours
Correct Answer:
C. 60 hours
Explanation:
Net rate = 1/12 - 1/15 = (5-4)/60 = 1/60. Time = 60 hours
