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## Homework Statement

1. The question asks for the value of P(~A and ~B) - What equation to use?

## The Attempt at a Solution

1. I am confused though, is P(~A and ~B) same as 1 - P(A and B)

or should I use, Pnot(A or B), and this is equivalent to 1 - P (A or B) ?

Extra question...

There is also another concept that I didn't fully grasp.

Lets say there is a lot of 20 pens.

and 60% that the lot has no defective pen.

30% contains 1 defective pen, and only 10% chance that the lot will have 2 defective pens.

So if a person selected 2 pens at random, and noticed they were NOT defective,

how does that change the probability of the rest of 18 pens still in the lot?? is it still 0.6 / 0.3 / 0.1 ?

Appreciate any help in advance.

Thanks