1. ## A simple question about probabiliy

My question is simple;

If I make a number of tests, let say 10, with only two possible results (true or false), and with 50% chance of getting true, 50% of getting false.

If I want to know the probabiliy of having 3 or less "true", it's relaively easy and I know how. But if I have to know he probability to get either 3 or less "true" or 3 or less "false", do I need to do something special or I can simply add the probabiliy of getting 3 or less "false" with the probability of getting 3 or less "true" ?

2. Originally Posted by AnnM
My question is simple;

If I make a number of tests, let say 10, with only two possible results (true or false), and with 50% chance of getting true, 50% of getting false.

If I want to know the probabiliy of having 3 or less "true", it's relaively easy and I know how. But if I have to know he probability to get either 3 or less "true" or 3 or less "false", do I need to do something special or I can simply add the probabiliy of getting 3 or less "false" with the probability of getting 3 or less "true" ?
Let n be the number of trues, then the number of falses is 10-n so:

P((n<=3) or (n>=6)) = P(n<=3) + P(n>=6)

so yes.

RonL