One member of the debate team is going to be chosen President. Each member is equally likely to be chosen. The probability that a girl is chosen is 2/3 the probability that a boy is chosen. If the debate team has 20 people, how many girls are there?

Question

Reiny · Accepted Answer

boys --- b
girls ---- g

b + g = 20 or g = 20-b

prob( boy is chosen) = b/20
prob(girl is chosen) = g/20
but g/20 = (2/3)(b/20
g/20 = b/30
3g = 2b
3(20-b) = 2b
60 - 3b = 2b
5b = 60
b = 12

so 12 boys and 8 girls

oobleck · Answer

for every 2 girls, there are 3 boys to choose from 2/5 of 20 is 8

bob · Answer

8 is right