Question

1.

Audrey has a bag of similar-sized red and green grapes. There are 12 red grapes and 13 green grapes in the bag. If the first 7 grapes she ate were green what is the probability that the 8th grapes she eats is green and the 9th grape she eats is red?

3/11
1/4
13/50
4/17

Answer 1

@mathmale

Answer 2

Hi, Chris,
If this person eats 7 of the 13 green grapes, then there are still 6 green grapes and 12 red ones left in the bag.
Given those numbers, what's the probability that the next grape pulled from the bag will be green?

Answer 3

4/17

Answer 4

But wouldn't there be 18 grapes in the bag when this person draws her next grape?
Out of those 18, how many are green?

Answer 5

13/50

Answer 6

Hope you agree with me that after this person eats 7 green grapes, there are 6 green grapes and 12 red ones left in the bag. Want to make sure we're on the same wavelength. Unsure of how you got 13/50.

Answer 7

so its 3/11

Answer 8

Chris, what I see here is that there are 6 green grapes in a total of 18 grapes, so that the chances of picking a green grape from those 18 is 6/18, or 3/9. Are you comfortable with this reasoning?

Answer 9

and 3/9 obviously equals 1/3.

Answer 10

So:

"The probability that Audrey will pick a green grape from a bag of 18, 6 of which are green and 12 are red, is 6/18."

Answer 11

Chris, we're getting there. Please let me know whether or not you want to continue with this problem solving. i'd like to help you to completion, but at the same time I have another person waiting for help.

Answer 12

I'm going to help that other person now, but if you reply, I'll also reply when free again. Fair enough?