A recent survey shows that the probability of a college student drinking alcohol is 0.6. Further, given that the student is over 21 years old, the probability of drinking alcohol is 0.8. It is also known that 30% of the college students are over 21 years old.
1. Of the students who are not over 21, what is the probability they drink alcohol?
a. 0.5143
b. 0.36
c. 0.24
d. 0.4857

option B is correct

Hence the probability students which are not 21 year old is 0.36

Step-by-step explanation:

Given :

Probability of college student drinking alcohol is 0.6

Probability that  over 21 year old drink is 0.8

And college has 0.3 of college student which are 0ver 21 year old.

To Find:

What is probability that students are not over 21 year will drink.

Solution:

(as the value in percentage we can consider any constant value for total college student, for Easy calculation).

Consider a college consist of 100 student .

Hence by give data,0.6 drink alcohol.

which means 60 students drink alcohol in college.

Total no .of drinker in college=60.

Now over the 21 age old students are 0.3

So total no of students which are over 21 yrs of age=30.

On which 0.8 drink alcohol

i.e. 80% of 30 students drink alcohol=0.8*30

=24 students.

So 24 students over 21 yrs of age drink alcohol.

So out of 60 alcohol drinking students,24 are of 21 years of age and rest will be below 21 yrs of age.

Probability of students not over 21 drinks =(60-24)/100

=36/100

=0.36

Hence the probability students which are not 21 year old is 0.36

27 +27 or 27times 2=54

the diffrence is 0