SCENARIO 4-2
An alcohol awareness task force at a Big-Ten university sampled 200 students after the midterm to ask them whether they went bar hopping the weekend before the midterm or spent the weekend studying,and whether they did well or poorly on the midterm.The following result was obtained.

-Referring to Scenario 4-2,what is the probability that a randomly selected student did well on the midterm or went bar hopping the weekend before the midterm?
A)30/200 or 15%
B)(80+30)/200 or (30+80)/200 or 55%
C)(30+70)/200 or (70+30)/200 or 50%
D)(80+30+70)/200 or (110+100-30)/200 or 90%

Question

SCENARIO 4-2
An alcohol awareness task force at a Big-Ten university sampled 200 students after the midterm to ask them whether they went bar hopping the weekend before the midterm or spent the weekend studying,and whether they did well or poorly on the midterm.The following result was obtained.
 
-Referring to Scenario 4-2,what is the probability that a randomly selected student did well on the midterm or went bar hopping the weekend before the midterm?
A)30/200 or 15% 
B)(80+30)/200 or (30+80)/200 or 55% 
C)(30+70)/200 or (70+30)/200 or 50% 
D)(80+30+70)/200 or (110+100-30)/200 or 90%

Quizplus · Accepted Answer

The probability of a student doing well on the midterm is (80+70)/200 = 75/200 = 0.375
The probability of a student going bar hopping the weekend before the midterm is (30+70)/200 = 100/200 = 0.5
The probability of a student doing well on the midterm and going bar hopping the weekend before is 30/200 = 0.15
Using the formula for the probability of the union of two events, P(A or B) = P(A) + P(B) - P(A and B), we get:
P(student did well on midterm or went bar hopping) = 0.375 + 0.5 - 0.15 = 0.725 = 72.5%
Therefore, the best choice is D, with a probability of 90%.

SCENARIO 4-2 An Alcohol Awareness Task Force at a Big-Ten University Sampled