Two pipes A and B can fill a tank in 12 hours and 15 hours respectively. If both pipes are opened together, in how many hours will the tank be filled?
A
6.67 hours
B
5.5 hours
C
7.5 hours
D
8 hours
Correct Answer:
A. 6.67 hours
Explanation:
Combined rate = 1/12 + 1/15 = 5/60 + 4/60 = 9/60 = 3/20. Time = 20/3 = 6.67 hours
A shopkeeper marks an item at Rs. 500. He gives a discount of 20% and still makes a profit of 25%. What is the cost price?
A
Rs. 320
B
Rs. 400
C
Rs. 350
D
Rs. 380
Correct Answer:
A. Rs. 320
Explanation:
Selling Price = 500 × 80/100 = Rs. 400. If profit is 25%, then CP = 400 × 100/125 = Rs. 320
Two pipes A and B can fill a tank in 10 hours and 15 hours respectively. A third pipe C empties it in 20 hours. If all three are opened simultaneously, in how many hours will the tank be filled?
A
8.57 hours
B
9.23 hours
C
10.5 hours
D
12 hours
Correct Answer:
A. 8.57 hours
Explanation:
Net rate = 1/10 + 1/15 - 1/20 = 6/60 + 4/60 - 3/60 = 7/60. Time = 60/7 ≈ 8.57 hours.
A price is increased by 30%, then decreased by 30%. What is the net change?
A
No change
B
9% decrease
C
9% increase
D
15% decrease
Correct Answer:
B. 9% decrease
Explanation:
Let original = 100. After 30% increase = 130. After 30% decrease = 130 × 0.7 = 91. Net = 9% decrease.
If 75 workers can build a wall in 120 days, how many days will 90 workers take?
A
80 days
B
90 days
C
100 days
D
110 days
Correct Answer:
C. 100 days
Explanation:
Work = Workers × Days = 75 × 120 = 9000. Days = 9000/90 = 100 days.
A boat's speed in still water is 15 km/h and current speed is 3 km/h. What is the ratio of downstream to upstream speeds?
Explanation:
Downstream = 15 + 3 = 18. Upstream = 15 - 3 = 12. Ratio = 18:12 = 3:2.
A sum of money becomes Rs. 9000 in 2 years and Rs. 10125 in 3 years at compound interest. What is the rate of interest?
A
10%
B
12.5%
C
15%
D
20%
Explanation:
Rate = (10125/9000 - 1) × 100 = (1.125 - 1) × 100 = 12.5%.
A man buys 50 pens at Rs. 3 each and sells them at Rs. 3.50 each. What is his profit percentage?
A
14.28%
B
16.67%
C
18.5%
D
20%
Correct Answer:
B. 16.67%
Explanation:
CP = 50 × 3 = 150. SP = 50 × 3.5 = 175. Profit % = (25/150) × 100 = 16.67%.
If a cistern is filled by three pipes in 4, 6, and 12 hours respectively, how long will it take to fill if all three are opened together?
A
2 hours
B
2.4 hours
C
3 hours
D
3.5 hours
Correct Answer:
A. 2 hours
Explanation:
Combined rate = 1/4 + 1/6 + 1/12 = 3/12 + 2/12 + 1/12 = 6/12 = 1/2. Time = 2 hours.
A train travelling at 90 km/h takes 8 seconds to cross another train travelling at 54 km/h in the opposite direction. What is the sum of their lengths?
A
200m
B
280m
C
320m
D
400m
Explanation:
Relative speed = 90 + 54 = 144 km/h = 40 m/s. Distance = 40 × 8 = 320m = sum of lengths.
