Question

 Supposed Ghana Standards Boards collected 40 electric bulbs from ELECTRO-NETS LTD for testing and 10 of them happened to be defective. If 4 of the bulbs were randomly selected one after the other, what is the probability that all the 4 bulbs are defective assumed sampling without replacements.

Answer 1

Let $X=$ the number of defective bulbs among 4 selected

$$P(X=4)=\dfrac{10}{40}(\dfrac{9}{39})(\dfrac{8}{38})(\dfrac{7}{37})=\dfrac{21}{9139}$$

$$\approx0.0023$$