Suppose that a jar contains 4 pens 2 black 1 blue and 1 red

Suppose that a jar contains 4 pens: 2 black, 1 blue, and 1 red. Three people select a pen at random from the jar, sign a document, and replace the pen in the jar before the next person selects a pen. What is the probability that none of the people use the red pen to sign the document?

Solution

sol) 4 pens: 2 black, 1 blue, and 1 red.

P(A person select red pen)=1/4
P(A person selects no red) = 1 - 1/4= 3/4

P(1st and 2nd and 3rd do not choose red) =3/4 * 3/4 *3/4 =27/64