GRE Probability and Statistics Concepts 2

Question 1

A fair six-sided die is rolled twice. What is the probability that the sum of the two rolls equals 7?

Accepted Answer

1/6

Answer

There are 6 ordered pairs summing to 7 out of 36 equally likely outcomes, giving 6/36 = 1/6.

Question 2

If events A and B are independent with P(A) = 0.4 and P(B) = 0.5, what is P(A and B)?

Accepted Answer

0.2

Answer

For independent events the joint probability is the product, 0.4 × 0.5 = 0.2.

Question 3

The mean of the data set {4, 8, 8, 10, 15} is closest to which value?

Accepted Answer

9

Answer

The sum is 45 and there are 5 values, so the mean is 45/5 = 9.

Question 4

A bag has 3 red and 2 blue marbles. Two are drawn without replacement. What is the probability both are red?

Accepted Answer

3/10

Answer

P = (3/5) × (2/4) = 6/20 = 3/10.

Question 5

What is the median of the set {12, 3, 7, 9, 15, 6}?

Accepted Answer

8

Answer

Sorted, the middle two values are 7 and 9, so the median is (7+9)/2 = 8.

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