Two friends can paddle a canoe at a rate of 6 km/h in still water. It takes them 1 h in total to paddle 2 km up a river and another 2 km back. Find the speed of the current, rounded to the nearest tenth.

The speed of the current is 3.5 km/h

Speed is the ratio of distance travelled to time taken. It is given by:

Speed = distance / time

Let a represent the speed of the current and t₁ represent the time spent paddling up and t₂ represent the time spent paddling back. Hence:

(6 - a)(t₁) = 2 km

t₁ = 2 / (6 - a)      (1)

(6 + a)(t₂) = 2 km

t₂ = 2 / (6 + a)   (2)

t₁ + t₂ = 1 hour

[2 / (6 - a)] + [2 / (6 + a)] = 1

12 + 2a + 12 - 2a = 36 - a²

a² - 12 = 0

a = 3.5 km/h

The speed of the current is 3.5 km/h

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The speed of the current is 3.5 km/h.

Step-by-step explanation:

When they move in the river, the speed of the canoe is:

Sc is the speed of the canoe and Sr is the speed of the current.

Sc + Sr (when they move in the same direction as the current)

Sc - Sr (when they move in the opposite direction as the current)

So we have that in one hour, they moved 2km and then they returned other 2km.

Now, using the relation:

Velocity*time = distance

we can write 1hour = T1 + T2 such that:

(Sc + Sr)*T1 = 2km

(Sc - Sr)*T2 = 2km

T1 + T2 = 1hour > T2 = 1h - T1

Sc = 6km/h.

So we can write this as two equations:

(6km/h + Sr)*T1 = 2km

(6km/h - Sr)*(1h - T1) = 2km.

Now, the first step will be isolate one of the variables in one equation, we can get:

T1 = 2km/(6km/h + Sr)

and replace it in the second equation:

(6km/h - Sr)*(1h -2km/(6km/h + Sr)) = 2km.

Now we solve this for Sr, i will ignore the units, so it is easier to read the math.

(6 - Sr) - 2*(6 - Sr)/(6 + Sr) = 2

(6 - Sr)*(6 + Sr) - 2*(6 - Sr) = 2*(6 + Sr)

6^2 - Sr^2 - 12 + 2*Sr - 12 - 2*Sr = 0

-Sr^2 + 36 -12 -12 = 0

-Sr^2 + 12 = 0

Sr = √12 = 3.5km/h

(where we take the positive value of the square root)

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the second option

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