Probability

Question 1

When 3 boys and 2 girls were added to the team, the ratio of boys to girls became 18:23. What was the ratio before?

Answer 1

The relationship cannot be determined, we don’t know how many boys or girls were (could be 18 and 23, but also 36 and 46).

Question 2

The probability of event E or event F, or both

Answer 2

P(E or F, or E&F) = P(E) + P(F) - P(E&F)

If E and F are mutually exclusive then P(E&F) = 0

Question 3

Events A and B are independent. What is the probability of A or B occurring.

Answer 3

P(A or B) = P(A) + P(B) - P(A and B) = P(A) + P(B) - P(A)*P(B)

Question 4

Approximately normally distributed data

Answer 4

• The mean, median and mode are all nearly equal.
• The data are grouped fairly symmetrically around the mean.
• About 2/3 of the data are within one standard deviation of the mean.
• Almost all of the data are within two standard deviations of the mean.