A box of 50 fuses contains five which are defective.
If I take a sample of 20 out of the box, calculate the probability
of there being at least two defective fuses.
There are: . possible sampes.
We have: .
The opposite of "at least 2 bad" is "0 bad or 1 bad".
0 bad, 20 good: .
1 bad, 19 good: .
. . Hence: .
You can crank it out . . . I'll wait in the car.