SOLUTION: Suppose that there are 4 coins in a box. Two of the coins are red on both sides, one of the coins is red on one side and black on the other side, and one of the coins is bla

Algebra ->  Probability-and-statistics -> SOLUTION: Suppose that there are 4 coins in a box. Two of the coins are red on both sides, one of the coins is red on one side and black on the other side, and one of the coins is bla      Log On


   

Question 1065867: Suppose that there are 4 coins in a box. Two of the coins are red on both sides,
one of the coins is red on one side and black on the other side, and one of the
coins is black on both sides. If a coin is drawn at random from the box and one
of its sides is red, what is the probability that both sides of the coin are red?
Found 2 solutions by Boreal, loveirng73:
Answer by Boreal(15235) About Me  (Show Source):
You can put this solution on YOUR website!
RR
RR
RB
BB
Given the coin has one red side, there is a 2/3 chance that both sides are red. It isn't 1/2, because we have eliminated one of the coins, thereby changing the probability.

Answer by loveirng73(1) About Me  (Show Source):
You can put this solution on YOUR website!
There are three coins left after eliminating the black/black coin. We have six sides that could be either red or black. Knowing one side is already red (as stated in the problem) then we are left with 5 sides. Of those five sides we could either have black or red. 4 out of five of those could be red as 1 out of 5 could be black. Therefore, the answer is 4/5.