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Q:

Amith can row a boat d km upstream and the same distance downstream in 5 hours 15 minutes. Also, he can row the boat 2d km upstream in 7 hours. How long will it take to row the same distance 2d km downstream for Amith ?

A) 4 hrs 10 min B) 3 hrs 15 min
C) 3 hrs 30 min D) 4 hrs 1 min

Answer:   C) 3 hrs 30 min



Explanation:

Let the speed of boat and stream be x and y kmph respectively.

According to question

d/x+y + d/x-y = 5h 15m or 21/4 hrs ......(i)

and 2d/x-y = 7...... (ii)

From eq. (i) and (ii)

2d/x+y = 7/2

Hence, Amith will take to row 2d km distance downstream in 7/2 hrs

= 3.5 hrs

= 3 hrs 30 min.

Q:

Find the speed of stream if a boat covers 36 km in downstream in 6 hours which is 3 hours less in covering the same distance in upstream?

A) 1.5 kmph B) 1 kmph
C) 0.75 kmph D) 0.5 kmph
 
Answer & Explanation Answer: B) 1 kmph

Explanation:

Speed of the boat upstream = 36/9 = 4 kmph

Speed of the boat in downstream = 36/6 = 6 kmph

Speed of stream = 6-4/2 = 1 kmph

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3 190
Q:

A boat can move 5 km/hr in still water. If the river is running at 1 km/hr, it takes it 75 min to move to a place and back. How far is the place?

A) 3 kms B) 5 kms
C) 6 kms D) 4 kms
 
Answer & Explanation Answer: A) 3 kms

Explanation:

Let the place be at a distance of 'd' kms

From the given data,

d5 - 1 + d5 + 1 = 7560 kmsd4 + d6 = 54

5d/12 = 5/4 => d = 3 kms.

 

Hence, the place is 3 kms far.

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3 534
Q:

If the boat goes 7 kms upstream in 42 min and speed of the stream is 3 kmph, then the speed of the boat in still water ?

A) 14 kmph B) 13 kmph
C) 12 kmph D) 11 kmph
 
Answer & Explanation Answer: B) 13 kmph

Explanation:

Given that, upstream distance = 7 kms

Upstream speed = 7/42 x 60 = 10 kms

Speed of the stream = 3 kmph

Let speed in still water = M kmph, then

Upstream speed = M - 3 = 10

=> M = 13 kmph.

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3 554
Q:

Sravan drove from home to a neighboring town at the speed of 50 km/h and on his returning journey, he drove at the speed of 45 km/h and also took an hour longer to reach home. What distance did he cover?

A) 350 kms B) 450 kms
C) 900 kms D) 700 kms
 
Answer & Explanation Answer: C) 900 kms

Explanation:

Let the distance he covered each way = d kms

According to the question,

d/45 - d/50 = 1

=> d = 450 kms.

 

Hence, the total distance he covered in his way = d + d = 2 d = 2 x 450 = 900 kms.

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5 473
Q:

A boat while travelling upstream covers a distance of 29 km at the speed of 6 km/h, whereas while travelling downstream it covers the same distance at a speed of 12 km/h. What is the speed of the boat in still water?

A) 6 kmph B) 8 kmph
C) 9 kmph D) 11 kmph
 
Answer & Explanation Answer: C) 9 kmph

Explanation:

Speed of boat in still water = 1/2 (12 + 6) = 9 kmph.

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5 1216
Q:

A Woman’s downstream swimming rate is thrice of her upstream swimming rate. If she covers 12 km upstream in 2.5 hours, what distance she will cover in 5 hours downstream?

 

A) 72 km B) 36 km
C) 56 km D) 42 km
 
Answer & Explanation Answer: A) 72 km

Explanation:

Rate of her upstream = 12/2.5 = 4.8 km/hr

Then, ATQ

Rate of downstream = 4.8 x 3 = 14.4 km/hr

 

Hence, the distance she covers downstream in 5 hrs = 14.4 x 5 = 72 kms.

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8 1540
Q:

A man went downstream for 28 km in a motor boat and immediately returned. It took the man twice as long to make the return trip. If the speed of the river flow were twice as high, the trip downstream and back would take 672 minutes. Find the speed of the boat in still water and the speed of the river flow.

A) 12 km/hr, 3 km/hr B) 9 km/hr, 3 km/hr
C) 8 km/hr, 2 km/hr D) 9 km/hr, 6 km/hr
 
Answer & Explanation Answer: B) 9 km/hr, 3 km/hr

Explanation:

Let the speed of the boat = p kmph

Let the speed of the river flow = q kmph

From the given data,

2 x 28p + q = 28p - q

 

=> 56p - 56q -28p - 28q = 0

=> 28p = 84q

=> p = 3q.

Now, given that if

283q + 2q + 283q - 2q = 67260=> 285q + 28q = 67260=> q = 3 kmph=> x  =3q = 9 kmph

 

Hence, the speed of the boat = p kmph = 9 kmph and the speed of the river flow = q kmph = 3 kmph.

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13 4047
Q:

Rajesh rows in still water with a speed of 4.5 kmph to go to a certain place and comes back. Find his average speed for the whole journey, if the river is flowing with a speed of 1.5 kmph?

A) 2 kmph B) 4 kmph
C) 6 kmph D) 8 kmph
 
Answer & Explanation Answer: B) 4 kmph

Explanation:

Let the distance in one direction = k kms

Speed in still water = 4.5 kmph

Speed of river = 1.5

Hence, speed in upstream = 4.5 - 1.5 = 3 kmph

Speed in downstream = 4.5 + 1.5 = 6 kmph

Time taken by Rajesh to row upwards = k/3 hrs

Time taken by Rajesh to row downwards = k/6 hrs

Now, required Average speed =Total distanceTotal speed = 2kk3 + k6 = 2k x 186k + 3k = 4 kmph 

 

Therefore, the average speed of the whole journey = 4kmph.

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7 1702