Probability of missing items

1. Jul 22, 2014

desmond iking

1. The problem statement, all variables and given/known data

i have problem of finding P(C) , why cant i use the method as in the photo to find P(C) beacuse 1-(all unused stamps are missing)= at least 1 use stamps is missing.

2. Relevant equations

3. The attempt at a solution

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2. Jul 22, 2014

Simon Bridge

C is the event at least one of the used stamps is missing.

"all unused stamps are missing" would mean there are 14 stamps missing - but the problem statement says only three are missing.

Did you mean, "all missing stamps are "unused"" - but that is not correct either since at least one of them has to be "used".

even C is the same as "at most two of the missing stamps are unused"

You need to comment your working.

3. Jul 22, 2014

desmond iking

Ya I mean all the 3 stamps missing are unused.

4. Jul 22, 2014

Simon Bridge

So if you write: D:=event all three missing stamps are unused, then you want to argue that P(C)=1-P(D), is that what you are saying?