Here's the third one . . .
There are: . ways to choose 3 fuses from a box.Q3) A factory produces fuses, which are packaged in boxes of 10.
Three are fuses selected at random from each box for inspection.
The box is rejected if at least one of these three fuses is defective.
What is the probability that a box containing five defective fuses will be rejected?
The opposite of "at least one defective" is "no defective" or "all good".
If the box has 5 defective and 5 good fuses,
. . there are: . ways to choose 3 good fuses.