Simple Probability: Understanding Odds of Picking Green Marbles from Bags

[Paddy]

I know this might be really simple, but I get easily confused.

CASE 1.

I have a bag with eight marbles, one of them is green and the remaining seven are red.

If you have to pick a random marble without looking, there is one in eight chances (12.5%) of lifting the green one.

Is this correct?

CASE 2.

I have three identical bags (like the one in case 1).

What are the chances of picking the three green ones? 3 in 24? (25%) this is how i though it would work out, but logically I predicted that it would have been more difficult to pick the three out of all the 24 (From three different bags), so I thought I was doing something wrong.

All help will be greatly appreciated.

 

[steven187]

Hi There,

In terms of CASE 1:

P(green)=1/8

In Terms of CASE 2:

E1=result of the first bag
E2=result of the second bag
E3=result of the third bag

P(E1nE2nE3)=(1/8)*(1/8)*(1/8)=1/512

This should be correct, hope it helps

regards Steven

 

[Paddy]

Thank you! That's what it was!

That does answer my doubt.