Directions: Each of the questions given below is followed by series of options among which you have to choose the best one. You can also review your choices by clicking into answer section.
16. The speed of a boat in still water is 8 kmph and the speed of the stream is 2 kmph. The boat travels to an island at a distance of 30 km, stays there for 2 hours and returns to the starting point at 5:00 pm. At what time did the boat start to the island?
A. 7:00 am
B. 8:00 am
C. 9:30 am
D. 6:15 am
Answer
Explanation:
Upstream speed(u) = b-s = 6 kmph,
Downstream speed(D. = b+s = 10 kmph ,
Time taken to travel upstream = 30/6 = 5 hours ,
Time taken to travel downstream = 30/10 = 3 hours
Time in the island = 2 hours
Total time = 10 hours,
Therefore, the boat should have started at 7 in the morning.
17. A man can row 9 km/hr in still water and he finds that it takes him thrice as much time to row up than as to row down the same distance in river. The speed of the current is :
A. 3 km/hr
B. 30 km/hr
C. 1 km/hr
D. 4 km/hr
Answer
Explanation:
No explanation
18. A man can row a boat at 10 kmph in still water. If the speed of the stream is 6 kmph, the time taken to row a distance of 80 km down the stream is : . [Central Excise ]
A. 8 hours
B. 10 hours
C. 5 hours
D. 20 hours
Answer
Explanation:
Speed downstream (10+6) km/hr 16 km/hr.
Time taken to cover 80 km downstream = (80/16) hrs = 5 hrs.
19. A man can row three quarters of a kilometer against the stream in 11 minutes and return in 7 minutes. The speed of the main still water is :
A. 2 km/hr
B. 3 km/hr
C. 4 km/hr
D. 5 km/hr
Answer
Explanation:
No explanation
20. A man rows 750 m in 675 seconds against the stream and returns in 7 and half minutes. His rowing speed in still water is:
A. 3 km/hr
B. 5 km/hr
C. 4 km/hr
D. 6 km/hr
Answer
Explanation:
Rate upstream = (750/675) = 10/9 m/sec
Rate downstream (750/450) m/sec = 5/3 m/sec.
Rate in still water = (1/2)*[(10/9) + (5/3)] m/sec. = 25/18 m/sec
= (25/18)*(18/5) kmPh = 5 kmph
21. The current of a stream runs at the rate of 4 km an hour. A boat goes 6 km and back to the starting point in 2 hours. The speed of the boat in still water is :
A. 6 km/hr
B. 7.5 km/hr
C. 8 km/hr
D. 6.8 km/hr
Answer: Option C
Answer
Explanation:
No explanation
22. In one hour, a boat goes 11 km/hr along the stream and 5 km/hr against the stream. The speed of the boat in still water (in km/hr) is:
A. 3 km/hr
B. 5 km/hr
C. 8 km/hr
D. 9 km/hr
Answer
Explanation:
Speed in still water = (1/2) (11 + 5) kmph = 8 kmph.
23. A swimmer covers a distance of 28 km against the current and 40 km in the direction of the current. If in each case he takes 4 hours, then the speed of the current is
A. 3 kmph
B. 1.5 kmph
C. 4.5 kmph
D. 8.5 kmph
Answer: Option B
Answer
Explanation:
No explanation
24. A Cistern is filled by pipe A in 8 hrs and the full Cistern can be leaked out by an exhaust pipe B in 12 hrs. If both the pipes are opened in what time the Cistern is full?
A. 12 hrs
B. 24 hrs
C. 16 hrs
D. 32 hrs
Answer : Option B
Explanation :
Pipe A can fill 1⁄8 of the cistern in 1 hour.
Pipe B can empty 1⁄12 of the cistern in 1 hour
Both Pipe A and B together can effectively fill 1⁄8-1⁄12= 1⁄24 of the cistern in 1 hour
i.e, the cistern will be full in 24 hrs.
Answer
Explanation:
Pipe A can fill 1⁄8 of the cistern in 1 hour.
Pipe B can empty 1⁄12 of the cistern in 1 hour
Both Pipe A and B together can effectively fill 1⁄8-1⁄12= 1⁄24 of the cistern in 1 hour
i.e, the cistern will be full in 24 hrs.
25. The time taken by a boat to travel upstream is twice the time taken by it to travel downstream. If the speed of the boat in still water is 9 kmph, find the rate of current.
A. 2 kmph
B. 2.5 kmph
C. 3 kmph
D. Data Insufficient
Answer
Explanation:
Let,
speed of boat as x kmph,
The downstream speed should be twice the upstream speed. so,9+x = 2*(9-x)
On solving we get,x=3
26. Speed of a boat in standing water is 6 km/hr and the speed of the stream is 1.5 km/hr A man rows to a place at a distance of 22.5 km and comes back to the starting point. The total time taken by him :
A. 6 hrs 30 min.
B. 8 hrs 24 min.
C. 8 hrs
D. 4 hrs 12 min.
Answer
Explanation:
No explanation
27. If a man rows 4 km downstream in 3 hours and 2 km upstream in 2 hours then how long will he take to cover 8 km in stationary (still) water?
A. 5 hours
B. 9 hours
C. 8 hours
D. none of these
Answer
Explanation:
Distance covered in downstream = 4 km
Time taken in downstream = 3 hours.
Rate of downstream = distance / time = a = 4km / 3 hours = 4/3 km/hr.
Distance covered in upstream = 2 km
Time taken in upstream = 2 hours.
Rate of upstream = distance / time = b = 2 km / 2 hours = 1 km/hr.
Speed in still water = (a + B./2 = (1/2)(4/3 + 1) km/hr = (1/2)(4 + 3)/3 = 7/6 km/hr.
Time Taken to cover 8 km in still water = distance / speed = 8 x 6/7 = 48 / 7 = 7 hours (approximately).
Hence the answer is option D.
28. Tap 'A' can fill the tank completely in 6 hrs while tap 'B' can empty it by 12 hrs. By mistake, the person forgot to close the tap 'B', As a result, both the taps, remained open. After 4 hrs, the person realized the mistake and immediately closed the tap 'B'. In how much time now onwards, would the tank be full?
A. 2 hours
B. 4 hours
C. 5 hours
D. 1 hour
Answer
Explanation:
Tap A can fill the tank completely in 6 hours
In 1 hour, Tap A can fill 1⁄6 of the tank
Tap B can empty the tank completely in 12 hours
In 1 hour, Tap B can empty 1⁄12 of the tank
i.e., In one hour, Tank A and B together can effectively fill 1⁄6 – 1⁄12 = 1⁄12 of the tank
In 4 hours, Tank A and B can effectively fill 1⁄12 × 4 = 1⁄3 of the tank.
Time taken to fill the remaining 1−(1/3)=2/3of the tank =(2/3)(1/6) = 4 hours
