The boat is moving along the river, the current speed is 3 km / h. The distance between the marinas is 100 km.

| August 6, 2021 | education

The boat is moving along the river, the current speed is 3 km / h. The distance between the marinas is 100 km. When moving along the river, the boat covers this distance in less than 4 hours, and when moving against the current, in more than 5 hours. What is the boat’s own speed?

Taking the speed of the boat as “k”, we write down the speeds upstream and downstream, respectively: (k + 3) and (k – 3). Now let us write down the inequalities according to the condition of the problem, knowing that the time “along” and “against” the flow is less than 4 and more than 5 hours.

100 / (k + 3) <4; 100 <4 * (k +3); 25 <k + 3; 22 <k; k> 22.

100 / (k – 3)> 5; 100> 5 * (k – 3); 20> k – 3; 23> k; k <23.

That is, we got a double inequality, which gives a restriction for the values of k:

23> k> 22. That is, any value of the boat speed from 22 (km / h) to 23 (km / h) is a solution.



One of the components of a person's success in our time is receiving modern high-quality education, mastering the knowledge, skills and abilities necessary for life in society. A person today needs to study almost all his life, mastering everything new and new, acquiring the necessary professional qualities.