Question

A shipment of 10 computers contains 2 with defects. Find the probability that a sample of size 2​, drawn from the ​10, will not contain a defective computer.

Answer 1

Answer:

$\frac{28}{45} .$

Step-by-step explanation:

way_1:

according to the condition the probability for the 1st computer is 8/10=4/5;

for the 2d computer is 7/9. Then the final probability is P=4/5 * 7/9=28/45;

way_2:

the required probability can be calculated according the formula:

$P=\frac{no-cases}{total-cases};$

then

$P=\frac{C^2_8}{C^2_{10}} =\frac{2!8!8!}{2!6!10!}=\frac{28}{45} .$