A sample of 5 accounts is chosen without replacement from a set of 20.
From past experience it is known that 20% of the accounts are in error.
What is the probability that not more than two errors will occur in the sample?
There are 20 accounts: .
There are: . possible samples.
We want the probability that there are:
. . 0 errors or 1 error or 2 errors.
0 E and 5 G: . ways.
1 E and 4 G: . ways.
2 E and 3 G: . ways.
Hence, there are: . ways to get 0, 1 or 2 Errors.