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9/10 Probability hat

There are four balls in a hat: one red, one blue, and two green. Your friend, Giuseppe, draws two balls and tells you that one of them is green. What are the chances that the other ball is also green?

Total possible options for the retrieved balls are:

G1G2, G1B, G1R, G2G1, G2B, G2R, BG1, BG2, BR, RG1, RG2, RB

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Comments (11)

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New
EZDsays...

1 in 5 is correct. If Giuseppe is not a liar.

The key word at the top is Probability (not outcomes).

You have to use All outcomes which there is 12 (if you numbered the two green balls 1 and 2).

The 12 outcomes are G1G2, G1B, G1R, G2G1, G2B, G2R, BG1, BG2, BR, RG1, RG2, RB.

When one of the balls is green (not knowing if the first or second pulled was green), this takes out two of the outcomes, BR and RB.

This leaves 10 outcomes. Of the ten left, two of the outcomes are both being green G1G2 and G2G1. That makes it 2/10 or 1/5.

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New
Yessays...

The answer is correct here. The probability of the first ball being green is 1/2. This would leave us with 1 green ball in the hat, and thus a chance of 1/3 to retrieve it. 1/2 x 1/3 is 1/6.

Now, what is the possibility of a ball NOT being green. The first ball drawn has a 1/2 chance of not being green. This would leave 1 non-green ball in the hat. The chance of drawing another non-green ball from the hat is 1/3. 1/2 x 1/3 is 1/6, leaving 5/6 possibilities where the ball is green. We know it’s a 1/6 chance of getting two green balls, 1/6 of 5/6 is 1/5.

The answer WOULD be 1/3 if we knew for certainty that the first ball was green or that the second ball was green, it could be either the first one or the second one or both.

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New
Marcosays...

naturally the answer is 1/3 but i'm wondering this is done on purpose to make us comment :p

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New
CKLsays...

Why so many people said that the answer of 1/5 is wrong?

G1, G2, R, and B

1) G1+G2 (same with G2+1 as you can not differentiate which is which)

2) G1+R

3) G1+B

4) G2+R

5) G2+R

So, those is said wrong can understand now?

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New
Camilasays...

I thought I could trust this, but instead the ANSWER is 1/5!!!!, tho its wrong and makes me think other question could be wrong do to incorrect scripting. The real answer is 1/3, but its wrong because the person that made this website is clearly bad at this topic in simple math.

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Regular
vmaxsays...

This question is getting a lot of attention as to whether the correct answer is 1/3 and not 1/5. (see comments below.) However the script is showing what it's intended to: 1/5.

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