Answer: 0.5143
Explanation:
Probability of students who are over 21 years old = 30% = 0.3
Probability of students who are under 21 years old = 100% - 30% = 70% = 0.7
Probability of drinking alcohol for over 21 = 80% = 0.8
Probability of not drinking alcohol for over 21 = 100%- 80% = 20% = 0.2
Let the probability of the students who are not over 21, that drink alcohol be p.
Total probability of a college student drinking alcohol = (0.3 × 0.8) + (0.7 × p)
0.6 = (0.3 × 0.8) + (0.7 × p)
0.6 = 0.24 + 0.7p
0.7p = 0.6 - 0.24
0.7p = 0.36
p = 0.36/0.7
p = 0.5143
The probability of the students who are not over 21, that drink alcohol is 0.5143.