Question

3/7 всех учеников 5 B класса выполнили проект только на компьютеое 2/7 написали только вручную а остальные выполнили проект и на компьютере и вручную. Проект только на компьютере и только вручную выполнило всего 20 учеников. Сколько учеников выполнили проект использовав оба способа?

Answer 1

5/7 Это 20 учеников (2/7+3/7=5/7)
20*5/7=4 ученика Это 1/7 класса
4:1/7=28 учеников в классе
28-20=8 человек и тем и другим способом

Answer 2

Problem Analysis

In this problem, we are given that 3/7 of all students in class 5B completed the project only on a computer, 2/7 completed it only by hand, and the rest completed it using both methods. We are also given that a total of 20 students completed the project using both methods. We need to determine how many students completed the project using both methods.

Solution

Let's denote the total number of students in class 5B as T.

According to the given information, 3/7 of the students completed the project only on a computer, which is equal to (3/7) * T.

Similarly, 2/7 of the students completed the project only by hand, which is equal to (2/7) * T.

We are also given that a total of 20 students completed the project using both methods.

Let's denote the number of students who completed the project using both methods as x.

Therefore, the equation representing the given information is:

(3/7) * T + (2/7) * T + x = 20

Simplifying the equation, we have:

(5/7) * T + x = 20

To find the value of x, we need to solve this equation.

Let's substitute some values for T and solve the equation.

Assuming there are 70 students in class 5B (this is just an example), we can substitute T = 70 into the equation:

(5/7) * 70 + x = 20

Simplifying further:

50 + x = 20

Subtracting 50 from both sides:

x = 20 - 50

x = -30

However, we cannot have a negative number of students who completed the project using both methods.

This means that our initial assumption of T = 70 is incorrect.

We need to find a value of T that makes x a positive integer.

Let's try different values of T until we find a solution.

Assuming T = 140 (this is just an example), we can substitute T = 140 into the equation:

(5/7) * 140 + x = 20

Simplifying further:

100 + x = 20

Subtracting 100 from both sides:

x = 20 - 100

x = -80

Again, we have a negative value for x.

Let's try one more value of T.

Assuming T = 210 (this is just an example), we can substitute T = 210 into the equation:

(5/7) * 210 + x = 20

Simplifying further:

150 + x = 20

Subtracting 150 from both sides:

x = 20 - 150

x = -130

Once again, we have a negative value for x.

Based on these calculations, it seems that there is no positive integer value of T that will result in a positive value for x.

Therefore, it is not possible to determine the number of students who completed the project using both methods with the given information.

Please note that this is a hypothetical example, and the actual values of T and x may be different. However, the approach to solving the problem remains the same.