Question

There are 20 boys and 15 girls in a class. The teacher calls thestudents' names randomly. What is the probability that the firststudent called is a boy and the second student is not a boy ifthe teacher calls the names with no repetition? Enter youranswer as a decimal rounded to the nearest hundredth.

Answer 1

The probability of the first student to be a boy is:

`(20)/(35)=(4)/(7)`

because there is 20 boys and 35 people. Next, for the second call there is just 19 boys and 34 people and 15 girls (no repetition). The probability of the second call to be a girl (not a boy) is:

`(15)/(34)`

Hence the probability of the two events together is:

`(4)/(7)*(15)/(34)=(30)/(119)=0.2521`

Hence the answer rounded to the nearest hundredth is: 0.25