HW Problem

[mutnauq]

I need a help with this question please:

Urn 1 contains 5 red balls & 3 black balls.
Urn 2 contains 3 red balls & 1 black ball.
Urn 3 contains 4 red balls & 2 black balls.
If an urn is selected at random and a ball is drawn, find the probability it will be red.

Thanks for helping.

[Shinjo]

If the urn is selected at random, can't you just treated as if all the balls were in 1 huge urn? I think it's just 12/18 right?

[mutnauq]

no, probability of getting each urn is 1/3

so

(1/3)(5/8)+(1/3)(3/4)+(1/3)(4/6)=49/72

I am thinking this way, but am not sre.

[JoAuSc]

no, probability of getting each urn is 1/3

so

(1/3)(5/8)+(1/3)(3/4)+(1/3)(4/6)=49/72

I am thinking this way, but am not sre.
sounds right.