Calculating Probability of Withdrawing 3 Discs in Any Order

[Joza]

How to calculate the probability of withdrawing 3 discs A B C from a bag, in any particular order? I just need the basic idea behind it

 

[mathman]

I assume there are no other discs in the bag. In that case, withdrawing the right disc first is 1/3. I will assume you keep it out. Then choosing the right second disc is 1/2. Therefore the overall probability is 1/6.