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Homework Statement
We have 8 white spheres and 5 black spheres in a box.We casually take out of the box a sphere and don't put it there again.Then we take two spheres out of the box.Find the probability that the spheres are both white.
Homework Equations
The Attempt at a Solution
So I put H1 --> the case where we have two white spheres so that means we have 6 white spheres and 5 black spheres
H2- One white sphere and one black sphere : we have 7 white spheres and 4 black spheres
H3 we take have two black spheres so we have 8 white and 3 black spheres
To find P(A) which is what I want I have to find the SUM of P(H)*P(A/H)
I find P(H1)= C (2/8)/C (2/13) and P(A/H1)=C (1/6)/C(1/11)
P(H2)=C (2/5)/ C( 2/13) and P(A/H2)= C (1/7)/ C(1/11)
and P(H3)= C (1/5) * C(1/8)/C (2/13).I find P (A/H3)=C(1/8)/C (1/11)
Now i multiply each P(H) with each P(A/H) and take their sum
BUT something tells me that I am wrong...am I wrong?