Problem:

In a fictional stats class, 40% of students are female, and the rest are male. Of the female students, 30% are less than 20 years old and 90% are less than 30 years old. Of the male students, half are less than 20 years old and 70% are less than 30 years old.

(a) Make a contingency table to describe these two variables

(b) Find the probability that a randomly selected studet is 30 years or older

(c) If a student is 20 years or older, what is the probability that the student is female?

(d) If a student is less than 30 years old, what is the probability that the student is 20 years or older?

My Thoughts:

(b) P(<30 years) = 1 - 0.78 = 0.22

(c) What I first did was find P(S2 given 'not A1'), but the answer doesn't make sense because the denominator ended up being smaller than the nominator.

(d) Do I solve this problem by doing 'not 20 years'?

In a fictional stats class, 40% of students are female, and the rest are male. Of the female students, 30% are less than 20 years old and 90% are less than 30 years old. Of the male students, half are less than 20 years old and 70% are less than 30 years old.

(a) Make a contingency table to describe these two variables

(b) Find the probability that a randomly selected studet is 30 years or older

(c) If a student is 20 years or older, what is the probability that the student is female?

(d) If a student is less than 30 years old, what is the probability that the student is 20 years or older?

My Thoughts:

(b) P(<30 years) = 1 - 0.78 = 0.22

(c) What I first did was find P(S2 given 'not A1'), but the answer doesn't make sense because the denominator ended up being smaller than the nominator.

(d) Do I solve this problem by doing 'not 20 years'?