Numbers
A boat's speed in still water is 15 km/h. Stream speed is 3 km/h. What is the ratio of downstream to upstream speed?
Downstream = 15 + 3 = 18. Upstream = 15 - 3 = 12. Ratio = 18:12 = 3:2
A train travels at 72 km/h. How many metres does it cover in 25 seconds?
A
400 m
B
500 m
C
600 m
D
700 m
Speed in m/s = 72 × 5/18 = 20 m/s. Distance = 20 × 25 = 500 m
Pipe A fills a tank in 24 minutes, Pipe B in 36 minutes. If both work together, how long to fill the tank?
A
12.8 minutes
B
14.4 minutes
C
15.6 minutes
D
16.2 minutes
Correct Answer:
B. 14.4 minutes
Combined rate = 1/24 + 1/36 = (3+2)/72 = 5/72. Time = 72/5 = 14.4 minutes
A man invests Rs. 8000 at 12% p.a. simple interest for 18 months. What amount does he receive?
A
Rs. 9440
B
Rs. 9600
C
Rs. 9680
D
Rs. 10000
Correct Answer:
A. Rs. 9440
SI = (8000 × 12 × 1.5)/100 = 1440. Amount = 8000 + 1440 = Rs. 9440
If 45% of a number equals 180, what is 80% of that number?
Number = 180/0.45 = 400. So 80% of 400 = 320
A shopkeeper marks goods 40% above cost price and offers 15% discount. What is his profit percentage?
Profit % = [(140 × 85)/100 - 100] = [119 - 100] = 19%
A merchant offers 30% discount on marked price. Even after discount, he makes 20% profit. If cost price is Rs. 700, what is the marked price?
A
Rs. 1000
B
Rs. 1100
C
Rs. 1200
D
Rs. 1400
Correct Answer:
C. Rs. 1200
CP = 700. For 20% profit, SP = 700 × 1.2 = 840. After 30% discount, SP = 0.7 × MP. So 840 = 0.7 × MP. MP = 840/0.7 = 1200.
A sum doubles in 5 years at simple interest. At the same rate, in how many years will it become 4 times?
A
10 years
B
12 years
C
15 years
D
20 years
Correct Answer:
C. 15 years
If sum doubles in 5 years: 2P = P + SI, so SI = P. Rate = (SI × 100) / (P × T) = (P × 100) / (P × 5) = 20%. For sum to become 4 times: 4P = P + SI, so SI = 3P. Time = (SI × 100) / (P × R) = (3P × 100) / (P × 20) = 15 years.
A is 50% more efficient than B. If B can complete a task in 24 days, how long will A take?
A
12 days
B
14 days
C
16 days
D
18 days
Correct Answer:
C. 16 days
B's rate = 1/24. A is 50% more efficient, so A's rate = 1.5 × (1/24) = 1.5/24 = 1/16. A takes 16 days.
The downstream speed of a boat is 20 km/h and upstream speed is 12 km/h. What is the boat's speed in still water?
A
14 km/h
B
16 km/h
C
18 km/h
D
20 km/h
Correct Answer:
B. 16 km/h
Boat speed = (Downstream + Upstream) / 2 = (20 + 12) / 2 = 32 / 2 = 16 km/h.
