Sat 2015 Practice Test #1 Answer Explanations

Choice C is correct.
The probability that a person from Group Y who 
recalled at least 1 dream was chosen at random from the group of all 
people who recalled at least 1 dream is equal to the number of people 
in Group Y who recalled at least 1 dream divided by the total number 
of people in the two groups who recalled at least 1 dream. The number 
of people in Group Y who recalled at least 1 dream is the sum of the 
11 people in Group Y who recalled 1 to 4 dreams and the 68 people in 
Group Y who recalled 5 or more dreams: 11 + 68 = 79. The total number 
of people who recalled at least 1 dream is the sum of the 79 people in 
Group Y who recalled at least 1 dream, the 28 people in Group X who 
recalled 1 to 4 dreams, and the 57 people in Group X who recalled 5 or 
_
more dreams: 79 + 28 + 57 = 164. Therefore, the probability is 79 
164.
Choice A is incorrect; it is the probability of choosing at random a 
person from Group Y who recalled 5 or more dreams. Choice B is 
incorrect; it is the probability of choosing at random a person from 
Group Y who recalled at least 1 dream. Choice D is incorrect; it is 

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the probability of choosing at random a person from the two groups 
combined who recalled at least 1 dream. 
QUESTION 22