A physical education teacher divided his class of 24 students into 2 groups the first group played football after 15 minutes he asked four students to join the first group at this time there were three times as many students in the first group than in the second group Record how many students were in the first group at the beginning
Let's denote the number of students in the first group at the beginning as x, and the number of students in the second group as y.
According to the problem:
x + y = 24
After 15 minutes, 4 students were added to the first group, so the number of students in the first group became x + 4. At this time, there were 3 times as many students in the first group than in the second group, so:
3(x + 4) = y
Now we have a system of two equations:
1) x + y = 24
2) 3(x + 4) = y
Let's solve the system of equations:
Expanding equation 2:
3x + 12 = y
Substitute equation 1 into equation 2:
3x + 12 = 24 - x
4x = 12
x = 3
Therefore, there were 3 students in the first group at the beginning.