A school debate team has four girls and six boys. A total of four of the team members will be chosen to participate in the district debate. What is the probability that two girls and two boys will be selected?

Procedure:

1) calculate the number of diferent teams of four members that can be formed (with the ten persons)

2) calculate the number of teams tha meet the specification (two girls and two boys)

3) Divide the positive events by the total number of events: this is the result of 2) by the result in 1)

Solution

1) the number of teams of four members that can be formed are:

10*9*8*7 / (4*3*2*1) = 210

2) Number of different teams with 2 boys and 2 girls = ways of chosing 2 boys * ways of chosing 2 girls

Ways of chosing 2 boys = 6*5/2 = 15

Ways of chosing 2 girls = 4*3/2 = 6

Number of different teams with 2 boys and 2 girls = 15 * 6 = 90

3) probability of choosing one of the 90 teams formed by 2 boys and 2 girls:

90/210 = 3/7