Question

Two ballpoint pens are selected at random from a box that contains 3 blue pens, 2 red pens, and 3 green pens. If X is the number of blue pens selected and Y is the number of red pens selected, find (a) the joint probability mass function, (b) P [(X, Y ) ∈ A], where A is the region {(x, y)|x + y ≤ 1}.

Answer 1

Answer:

a) f(x,y) =$\frac{\binom{3}{x}\binom{2}{y}\binom{3}{2-x-y}}{\binom{8}{2}}$ ;   x = 0, 1 , 2;  y = 0, 1 , 2; 0 ≤ x+y ≥ 2

b) = $\frac{9}{14}$

Step-by-step explanation:

joint probability is a function that characterizes the distribution of a random variable. If X and Y be two random variables then the joint probability will be P(X = x, Y=y)

Given Data,

X = The number of blue Pens

Y = The number of red Pens

a)

possible outcomes(X, Y) are (0, 0), (0, 1), (1, 0), (1, 1), (0, 2), (2,0)

Please refer fig. also

total number ways of selecting any 2 pens = $\binom{8}{2}$= $\frac{8!}{2! 6!}$ =28

f(x,y) = $\frac{\binom{3}{x}\binom{2}{y}\binom{3}{2-x-y}}{\binom{8}{2}}$ ;   x = 0, 1 , 2;  y = 0, 1 , 2; 0 ≤ x+y ≥ 2

b)

P(X,Y)∈A = P(X + Y ≤ 1)

= P(0,0) + P(1,0) + P(0,1)

= $\frac{3}{28}$ + $\frac{3}{14}$ + $\frac{9}{28}$

= $\frac{9}{14}$