A red marble is selected at random from a bag of 2 blue and 9 red marbles and not replaced. What is the probability that a second mable will be red?

Question

This is a word problem from my book, just wondering if anyone can give some help! Thank you!

Answer 1

Hi Beau,

 

It seems to me that if one red marble is already gone, there are 8 red marbles left out of a total of 10 marbles.

 

So the probability of drawing a second red marble is 8 out 10 or 0.8.

 

Dan

Answer 2

Hi Beau,

 

The probability of an event is the number of ways that event can occur divided by the total number of possible events. In your case, it is the number of red marbles divided by the total number of marbles.

 

For the first marble, the probability of red is 9/(9+2) = 9/11.

For the second marble, the probabilities are a little difference because the first marble was drawn without being replaced. Since the first marble red, there is now one less red marble that can be chosen on the second draw. So the probability is now: 8/10.

 

Hope that helps.