# Math Help - probability law of total porbab, problem.

1. ## probability law of total porbab, problem.

hi,

thinking total law of prob here, but dunno where to begin! thanks

a box will contain 10 balls. you turn a spinner, with 6 sides. if it lands on an even side, you put that number of green balls into the box, if it lands on an odd number, that number of black balls is placed in the box, (rest are of other colour).
calc all probs of selecting a black ball if randomly selecting one from the box (done this)
so say it landed on a 5, 5 black balls would be in the box, and because the box has 10 balls, the other 5 are green etc, their are always 10 in their

if a black ball is selected, what is the prob that the spinner landed on a 6?

using the formulae of total law of probability, i've got:

P(6|B) P(B) = P(B|6) P(6)

but don't know where to go.

thanks again guys!

2. solved it, thanks anyway