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) +
1
P(X=1) +
2
P(X=2) +
3
P(X=3) +
4
P(X=4) +
5
P(X=5) +
6
P(X=6)
= 248832/4826809 + 220736/4826809 +
3
1728/4826809 +
4
144/4826809 +
5
12/4826809 +
6
1/4826809
= 296130/4826809
E(X2) = 02P(X=0) +
12
P(X=1) +
22
P(X=2) +
32
P(X=3) +
42
P(X=4) +
52
P(X=5) +
62
P(X=6)
= 248832/4826809 + 420736/4826809 +
9
1728/4826809 +
16
144/4826809 +
25
12/4826809 +
36
1/4826809
= 349968/4826809
Var(X) = E(X2) - [E(X)]2 = 296130/4826809 - (349968/4826809)2 = 1306885348146/23298085122481 = 0.0561