Question

две бригады покрасили полы за 15ч. Первая бригада, работая одна, могла бы покрасить полы за 20ч. За сколько часов покрасила бы полы вторая бригада, работая одна?

Answer 1

1) 1:15=1/15 часть работы будет выполнена обеими бригадами за 1 час
2) 1 :20=1/20 часть работы будет выполнена первой бригадой за 1 час
3) 1/15-1/20=1/60  часть работы будет выполнена второй бригадой за 1 час
4)1:1/60=за 60 часов покрасила бы вторая бригада работая одна

Answer 2

Problem Analysis

We are given that two teams painted the floors in 15 hours. The first team, working alone, would have taken 20 hours to paint the floors. We need to determine how many hours it would take for the second team to paint the floors alone.

Solution

Let's assume that the second team can paint the floors in x hours when working alone.

The rate at which the first team paints the floors is 1/20 of the floors per hour. The rate at which the second team paints the floors is 1/x of the floors per hour.

When both teams work together, their combined rate is 1/15 of the floors per hour.

According to the problem, the combined rate of both teams is equal to the sum of their individual rates. Therefore, we can set up the following equation:

1/20 + 1/x = 1/15

To solve for x, we can multiply both sides of the equation by 60x (the least common multiple of 20, 15, and x) to eliminate the denominators:

3x + 60 = 4x

Simplifying the equation, we find:

60 = x

Therefore, the second team would take 60 hours to paint the floors alone.

Answer

The second team would take 60 hours to paint the floors alone.