In: Statistics and Probability
draw six cards at random from a deck of 52 playing cards 60 times with replacement. Let X be the number of queen cards.
Find the probability distribution of X and Var (x)
Probability of drawing a queen at one random draw = 4/52 = 1/13
Probability of not drawing a queen at one random draw = 1 - 1/13 = 12/13
Mass points of X are :- 0,1,2,3,4,5,6
P(X=0) = Probability of not drawing a queen at 6 random draws = (12/13)6 = 2985984/4826809
P(X=1) = Probability of drawing a queen at 1 random draw and not drawing a queen at 5 random draws = (1/13)(12/13)5 = 248832/4826809
P(X=2) = Probability of drawing a queen at 2 random draws and not drawing a queen at 4 random draws =(1/13)2(12/13)4
= 20736/4826809
P(X=3) = Probability of drawing a queen at 3 random draws and not drawing a queen at 3 random draws = (1/13)3(12/13)3
= 1728/4826809
P(X=4) = Probability of drawing a queen at 4 random draws and not drawing a queen at 2 random draws = (1/13)4(12/13)2
= 144/4826809
P(X=5) = Probability of drawing a queen at 5 random draws and not drawing a queen at 1 random draw = (1/13)5(12/13)
= 12/4826809
P(X=6) = Probability of drawing a queen at 6 random draws = (1/13)6 = 1/4826809
E(X) = 0P(X=0) + 1P(X=1) + 2P(X=2) + 3P(X=3) + 4P(X=4) + 5P(X=5) + 6P(X=6)
= 248832/4826809 + 220736/4826809 + 31728/4826809 + 4144/4826809 + 512/4826809 + 61/4826809
= 296130/4826809
E(X2) = 02P(X=0) + 12P(X=1) + 22P(X=2) + 32P(X=3) + 42P(X=4) + 52P(X=5) + 62P(X=6)
= 248832/4826809 + 420736/4826809 + 91728/4826809 + 16144/4826809 + 2512/4826809 + 361/4826809
= 349968/4826809
Var(X) = E(X2) - [E(X)]2 = 296130/4826809 - (349968/4826809)2 = 1306885348146/23298085122481 = 0.0561