# Aptitude - Boats and Streams - Discussion

Discussion Forum : Boats and Streams - General Questions (Q.No. 2)

2.

A man's speed with the current is 15 km/hr and the speed of the current is 2.5 km/hr. The man's speed against the current is:

Answer: Option

Explanation:

Man's rate in still water = (15 - 2.5) km/hr = 12.5 km/hr.

Man's rate against the current = (12.5 - 2.5) km/hr = 10 km/hr.

Discussion:

72 comments Page 1 of 8.
Ritesh jha said:
2 months ago

Not yet understand the solution. Please help me to get this.

Aathira said:
7 months ago

@All.

Against the current - upstream.

Along the current - downstream.

If they mentioned the question like "the speed of the man is...", definitely the answer will be 12.5 km/hr, ie. upstream = speed of the man - speed of the current = 15-2.5=12.5 km/hr.

But,

The question was like "Speed of the man with the current".

ie., 15km/hr is the summation of the speed of the man and the current. so we need to subtract the speed of the current from 15, to know man's speed in water.

ie., 15 - 2.5 = 12.5 => man's speed.

After the above step, we can easily find the man's speed against the current by using the formula below:

upstream = speed of the man - speed of the current.

= 12.5 - 2.5 = 10 km/hr.

Against the current - upstream.

Along the current - downstream.

If they mentioned the question like "the speed of the man is...", definitely the answer will be 12.5 km/hr, ie. upstream = speed of the man - speed of the current = 15-2.5=12.5 km/hr.

But,

The question was like "Speed of the man with the current".

ie., 15km/hr is the summation of the speed of the man and the current. so we need to subtract the speed of the current from 15, to know man's speed in water.

ie., 15 - 2.5 = 12.5 => man's speed.

After the above step, we can easily find the man's speed against the current by using the formula below:

upstream = speed of the man - speed of the current.

= 12.5 - 2.5 = 10 km/hr.

(28)

Keerthana said:
12 months ago

You are right @Balaji.

Thank you for explaining.

Thank you for explaining.

(3)

Chala Alemu Feyisa said:
1 year ago

I am not understanding this. Please explain me.

(2)

Tejas said:
1 year ago

Yes, you are right @Balaji.

Good Explanation, Thanks a lot.

Good Explanation, Thanks a lot.

(1)

Ayaan mansoori said:
2 years ago

Yes, you are right. Thanks @Balaji.

Anonymous said:
2 years ago

@All.

Suppose you are riding a boat which is arriving to the beach. Naturally, the waves are in the same direction of your boat. Dont you feel easy to drive it then. Hence, the speed of waves/current supplement your boat speed. Then, it is called going downstream or going with the waves/current. Hence, By thinking vice-versa we know that we'd have to subtract the speed of the stream

Suppose you are riding a boat which is arriving to the beach. Naturally, the waves are in the same direction of your boat. Dont you feel easy to drive it then. Hence, the speed of waves/current supplement your boat speed. Then, it is called going downstream or going with the waves/current. Hence, By thinking vice-versa we know that we'd have to subtract the speed of the stream

Rathod Vamshi said:
2 years ago

Here, the given speed of the man 15 km/hr but not given directly speed of the man 15 km/hr then we subtract 15-2.5 then we get the speed of the man.

(2)

Arun said:
2 years ago

Hey guys.

If they said the man speed is ..the answer is 12.5...but;

The man speed with the current.

So the 15 km/hr have ( man speed + Current speed).

So the answer is 10km/hr.

If they said the man speed is ..the answer is 12.5...but;

The man speed with the current.

So the 15 km/hr have ( man speed + Current speed).

So the answer is 10km/hr.

(2)

Himanth said:
3 years ago

Here time has given 8hr 48min upstream, 4 hours downstream.

T=8 4/5 (While changing min to hours 48/60=4/5)

Upstream speed = Distance/time.

x-y = D/8.4/5.

D = 44/5(x-y)-------> (1)

Now downstream speed=Distance/time.

X+y=D/4,

D=4(X+y) -----------> (2)

Equate eq 1 and 2.

44/5(x-y) = 4(X+y).

24x = 64y.

X/y = 64/24,

X/y = 8:3.

T=8 4/5 (While changing min to hours 48/60=4/5)

Upstream speed = Distance/time.

x-y = D/8.4/5.

D = 44/5(x-y)-------> (1)

Now downstream speed=Distance/time.

X+y=D/4,

D=4(X+y) -----------> (2)

Equate eq 1 and 2.

44/5(x-y) = 4(X+y).

24x = 64y.

X/y = 64/24,

X/y = 8:3.

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