Statistics Questions? help!?

1) Assume that 75% of Stats student studied for a test. If 40% of those who studied got an A, and only 10% of those who didn't study got an A, what is the probability that someone who got an A actually studied?








2) Assume the heights if high school basketball players are normally distributed, For boys the mean is 74 inches with a std. dev. of 4.5 in., while for the girls the mean in 70 in. w/ a std. dev. of 3 in. At a mixed 2 - on - 2 tournament teams are formed by randomly pairing boys with girls as teammates.





a) On average, how much taller do you expect the boys to be?





b) What will be the std. dev. of the difference in teammates height?





c) On what fraction of teams would you expect the girl to be taller than the boy?

Statistics Questions? help!?
For question 1) make a table:


Studied %26amp; A 75% x 40% = 30%


Studied %26amp; not A 75% x 60% = 45%


Not Studied %26amp; A 25% x 10% = 2.5%


Not Studied %26amp; not A 25% x 90% = 22.5%





So 30% + 2.5% =32.5% of the students got an A and


30%/32.5% = 92.3% actually studied.





2a) 74-70 =4 inches


b) std(team)^2 = std(boy)^2 + std(girl)^2 = 29.25


std(team) = 5.4 inches


c) z=4/5.4 = 0.74 Look up the probability in a table.