"Matching balls": Why is the probability for the first ball 1 and not 1/10?

Link

http://gre.magoosh.com/questions/844

Question

Why is the probability for the first ball 1 and not 1/10?

 

Answer

If we were looking for the possibility of Anne picking a specific ball , then we would use 1/10 for that probability because there are ten possible outcomes but only one desired outcome.

Say, for example, the question asked for the probability of both Ann and Jane picking the three ball. There's only one three, so that's 1/10 * 1/10.

But we're not looking for any one specific ball the first time; instead, any ball will meet our requirements. So there are ten desired outcomes over ten possible outcomes, i.e. 10/10, which equals 1.

If any outcome works, the probability is always 1.

prompt_id=844