Question

An urn contains 10 white balls and 5 blue balls. Draws are made repeatedly from the urn as follows. On each draw, a ball is drawn and its color noted; then it is replaced in the urn along with 3 more balls of its color.

Find the chance that the second ball drawn is blue, given that the first ball drawn is blue.

Answer 1

First we have 10 white balls and 5 blue balls. After drawing a blue ball, recall it is replaced and then supplemented with 3 more blue balls -- so now we have 10 white balls and 8 blue balls. The probability that the next draw yields blue is then merely \(\dfrac8{18}=\dfrac49\)

Answer 2

thanx