Question

Скорость корабля 18 км/ч. Лодка прошла 84 км по озеру за 2 часа и по реке за 3 часа. Какова скорость реки? Помогитеее!!!​

Answer 1

Ответ:

2 км/ч

Пошаговое объяснение:

1) 18 * 2 = 36(км)- прошел по озеру

2) 84 - 36 = 48(км)- прошел по реке

3) 48 : 3 = 16(км/ч)- скорость по реке

4) 18 - 16 = 2(км/ч)- скорость течения реки

Answer 2

Problem Analysis

We are given that a boat traveled 84 km on a lake in 2 hours and then traveled the same distance on a river in 3 hours. We need to determine the speed of the river.

Solution

Let's assume the speed of the boat in still water is x km/h, and the speed of the river is y km/h.

When the boat is traveling on the lake, it is moving with the current, so the effective speed is the sum of the boat's speed and the speed of the river: (x + y) km/h.

We are given that the boat traveled 84 km on the lake in 2 hours, so we can set up the equation:

Distance = Speed × Time

Substituting the values we have:

84 = (x + y) × 2

Simplifying the equation, we get:

42 = x + y ----(1)

When the boat is traveling on the river, it is moving against the current, so the effective speed is the difference between the boat's speed and the speed of the river: (x - y) km/h.

We are given that the boat traveled 84 km on the river in 3 hours, so we can set up the equation:

Distance = Speed × Time

Substituting the values we have:

84 = (x - y) × 3

Simplifying the equation, we get:

28 = x - y ----(2)

Now we have a system of two equations with two variables. We can solve this system of equations to find the values of x and y.

Let's solve the system of equations (1) and (2) using the substitution method:

From equation (1), we have:

x = 42 - y

Substituting this value of x into equation (2), we get:

28 = (42 - y) - y

Simplifying the equation, we get:

28 = 42 - 2y

Rearranging the equation, we get:

2y = 42 - 28

Simplifying further, we get:

2y = 14

Dividing both sides of the equation by 2, we get:

y = 7

Therefore, the speed of the river is 7 km/h.

Answer

The speed of the river is 7 km/h.