Question

Расстояние между двумя пристанями лодка проплывает по течению реки за 1,2 часа, а против течения реки - за 1,8 часа.За сколько времени проплывет это растояние плот по реке? Решите пожалуйста задачу в долгу не останусь... Наверное.

Answer 1

скорость течения - х, скорость лодки - у, уравнение -

(х+у)*1,2=(х-у)*1,8

1,2х+1,2у=1,8х-1,8у

0,6х=3у

или х=3у/0,6=5у

 

т.е. скорость лодки в 5 раз больше скорости реки

 

если бы не было течения, лодка проплыла бы это расстояние за (1,2+1,8)/2=1,5 часа

плот, соответственно, в 5 раз дольше

 

1,5*5=7,5 часов

Answer 2

Problem Analysis

We are given that a boat can travel between two docks on a river in 1.2 hours when traveling with the current and in 1.8 hours when traveling against the current. We need to determine how long it will take for a raft to travel the same distance on the river.

Solution

Let's assume that the distance between the two docks is d.

When the boat is traveling with the current, it takes 1.2 hours to cover the distance d. This means that the speed of the boat relative to the water is d/1.2.

When the boat is traveling against the current, it takes 1.8 hours to cover the same distance d. This means that the speed of the boat relative to the water is d/1.8.

Let's denote the speed of the current as c.

When the boat is traveling with the current, the effective speed of the boat is the sum of its speed relative to the water and the speed