Basic probablity question.

Three coins are tossed. Find the probabilikty that they all land heads up for each known condition.

P(X|Y)=P(X)*P(Y)/P(Y)

6. The first coin shows a head.

**My work: **2*2*2=8 possibilities

8 Pr 2=56 ways to choose that so it fits that one shows a head..

(1/56)*(1/8)/(1/8)=1/56?

7. At least one coin shows a head.

8. At least two coins show heads

...that's all I know how to work out so far.

Also, if somebody could explain how this logically makes sense, I'd really appreciate it! (Something like a tangible example or whatnot would be great)