Question ID: 89f20d9e
Assessment Test Domain Skill Difficulty
SAT Math Problem-Solving and
Data Analysis
Probability and
conditional probability
Hard
Question
The table summarizes the distribution of age and assigned group for participants in a study.
–
years
–
years years
Total
Group A
Group B
Group C
Total
One of these participants will be selected at random. What is the probability of selecting a participant from group A, given that the participant is
at least 10 years of age?
Answer
A.
B.
C.
D.
Correct Answer: B
Rationale
Choice B is correct. Since the participant will be selected at random, the probability of selecting a participant from group A, given that the
participant is at least years of age, is equal to the number of participants from group A who are at least
years of age divided by the total
number of participants who are at least years of age. Based on the table, in group A, there are participants who are
–
years of age
and par ticipants who are
years of age. Therefore, there are a total of
, or, participants in group A who are at least years of
age. Based on the table, of the total number of participants, there are participants who are
–
years of age and participants who are
years of age. Therefore, a total of , or , of the participants are at least years of age. Thus, the probability of selecting a
participant from group A, given that the participant is at least years of age, is , or .
Choice A is incorrect. This is the number of participants from group A who are at least years of age divided by the total number of
participants, rather than divided by the number of participants who are at least years of age.
Choice C is incorrect. This is the probability of randomly selecting a participant from group A, given that the participant is
–
years of age,
rather than given that the participant is at least years of age.
Choice D is incorrect. This is the probability of randomly selecting a participant who is at least years of age, given that the participant is in
group A.