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- Question
- A person can row 7 1/ 2 km/h in still water. It takes him twice as long to row up a distance as to row down the same distance. Find the speed of the stream?
Options- A. 2 km/h
- B. 2.2 km/h
- C. 2.5 km/h
- D. 2.7 km/h
- Correct Answer
- 2.5 km/h
ExplanationSpeed upstream + Speed downstream = 2 x 71/2 = 15 km/h
Since, the time taken is in the ratio 2 : 1
hence the speed will be in the ratio 1 : 2
? Speed upstream = (1/3) x 15 = 5 km/h
and speed downstream = (2/3) x 15 = 10 km/h
? Speed of stream = (10 - 5)/2 = 2.5 km/h - 1. A thief running at 8 km/h is chased by a policeman whose speed is 10 km/h. If the thief is 100 m ahead of the policeman, then the time required for the policeman to catch the thief will be
Options- A. 2 min
- B. 3 min
- C. 4 min
- D. 6 min Discuss
- 2. Starting from his house, one day a student walks at a speed of 3 km/h and reaches his school 5 min late. Next day he increases his speed by 1 km/h and reaches the school 3 min early. How far is the school from his house?
Options- A. 1.6 km
- B. 1.24 km
- C. 1.36 km
- D. 1.8 km Discuss
- 3. A train running at 8/11 of its own speed reached a place in 5 1/ 2 h. How much time could be saved, if the train would have run as its own speed?
Options- A. 21/2 h
- B. 2 h
- C. 11/2 h
- D. 1 h Discuss
- 4. A car during its journey travels 30 min at a speed of 40 km/h, another 45 min at a speed of 60 km/h and 2 h at a speed of 70 km/h. Find its average speed?
Options- A. 58 km/h
- B. 63 km/h
- C. 67 km/h
- D. 71 km / h Discuss
- 5. Walking 5/7 of his usual rate, a boy reaches his school 6 min late. Find his usual time to reach the school?
Options- A. 10 min
- B. 12 min
- C. 15 min
- D. 18 min Discuss
- 6. A streamer goes downstream from one port to another in 4 h. It covers the same distance upstream in 5 h. If the speed of the stream is 2 km/h , find the distance between the two ports?
Options- A. 50 km/h
- B. 60 km/h
- C. 70 km/h
- D. 80 km/h Discuss
- 7. The current of a stream runs at 1 km/h. A motorboat goes 35 km upstream and back again at the starting point in 12 h. What is the speed of motorboat in still water?
Options- A. 7 km/h
- B. 4 km/h
- C. 6 km/h
- D. 5 km/h Discuss
- 8. The speed of a motorboat is 30 km/h. It starts from Mumbai at 6 am and reaches Goa at 8 am. Same day, it starts from Goa at 12 pm and reaches Mumbai at 4 pm. Find the the speed of stream.
Options- A. 8.5 km/h
- B. 12 km/h
- C. 10 km/h
- D. 11.5 km/h Discuss
- 9. At his usual rowing speed, Kapil can travel 12 miles downstream in a certain river in 6 h less than he takes to travel the same distance upstream. But, If he could double his usual rowing speed for his 24 miles round trip, the downstream 12 miles would then take only 1 h less than the upstream 12 miles. What is the speed of the current?
Options- A. 22/3 mile/h
- B. 32/3 mile/h
- C. 52/3 mile/h
- D. 72/3 mile/h Discuss
- 10. A person riding a bike crosses a bridge with a speed of 54 km/h. What is the length of the bridge, if he takes 4 min to cross the bridge?
Options- A. 3600 m
- B. 2800 m
- C. 3500 m
- D. 4500 m Discuss
Time and Distance problems
Search Results
Correct Answer: 3 min
Explanation:
Relative speed of policeman with thief = (10 - 8) = 2 km/h
Now, time taken to cover 100 m with speed of 2 km/h or 2000 m/h
Now, Speed = Distance / Time
? Time = D/S = 100/2000
= 1/20 h or 60/20 min = 3 min
Correct Answer: 1.6 km
Explanation:
Let the distance be D km
Difference in timings = 8 min = 8/60 h = 2/15 h
? D/3 - D/4 = 2/15
? D/12 = 2/15
? D = 2 x 12/15 = 1.6 km
Correct Answer: 11/2 h
Explanation:
New speed = 8/11 of usual speed
New time = 11/8 of usual time
? 11/8 of usual time = 11/2 h
? Usual time = (11 x 8)/(2 x 11) = 4 h
? Time saved = 51/2- 4
= 11/2
Correct Answer: 63 km/h
Explanation:
Average speed = [(30/60) x 40 + (45/60) x 60 + (2 x 70)] / [(30/60) + (45/60) + 2]
= (20 + 45 + 140)/[(30 + 45 + 120)/60]
= (205/195) x 60 km/h
= 63.07 km/h
= 63 km/h
Correct Answer: 15 min
Explanation:
Since, the boys now walks at 5/7 of usual speed, so he will take 7/5 of his usual time.
? Extra time = (7/5 - 1) x Usual time = 6 min (known)
? 2/5 x Usual time = 6
? Usual time = 15 min
Correct Answer: 80 km/h
Explanation:
Let the distance between the two ports = L km
Then, speed downstream = L/4
and speed upstream = L/5
? Speed of the stream = 1/2(L/4 - L/5)
? 1/2[(5L - 4L)/20] = 2
? L = 80 km
Correct Answer: 6 km/h
Explanation:
Let the speed of boat in still water be V km/h. Then,
35/(V - 1) + 35/(V + 1) = 12
? 35(V + 1 + V - 1) = 12(V2 - 1)
? 6V2 - 35V - 6 = 0
? (V - 6)(6V + 1) = 0
? V = 6 (V = - 1/6 is not possible)
So, speed of boat in still water is 6 km/h.
Correct Answer: 10 km/h
Explanation:
Clearly, motorboat takes 2 h go from Mumbai to Goa and 4 h to go from Goa to Mumbai. i.e.,
Time taken to row upstream = 2 x Time taken to row downstream
? n = 2
Let the speed of stream be V km/h.
According to the formula,
Speed of boat = V(n + 1)/(n - 1)
? 30 = V(2 + 1)/(2 - 1)
? V = 30/3 = 10 km/h
Correct Answer: 22/3 mile/h
Explanation:
Let speed of Kapil in still water = x
and speed of the current= y
? Speed upstream = (x - y)
and speed downstream = (x + y)
According to the question,
12/(x - y) - 12/(x + y) = 6
? 6(x2 - y2) = 24y
? x2 - y2 = 4y
? x2 = 4y + y2 ....(i)
Again, 12/(2x - y) - 12/(2x + y) = 1
? 4x2 - y2 = 24y
? x2 = (24y + y2)/4 ....(ii)
From Eqs. (i) and (ii), we get
4y + y2 = (24y + y2)/4
? 16y +4y2 = 24y + y2
? 3y2 = 8y
? y = 8/3 = 22/3 mile/h
Correct Answer: 3600 m
Explanation:
Length of the bridge = Distance travelled by the person in 4 min = Speed x Time
Speed = 54 km/h = 54 x (5/18) = 3 x 5 = 15 m/s
Time = 4 min = 4 x 60 = 240 s
? Required length = 15 x 240 = 3600 m
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