Question

There are $7$ defective items in a sample of $35$ items. Find the probability that an item chosen at random is non-defective.

Answer 1

Given, number of items $=35$, $n\left(S\right)=35$

Defective items $=7$

Non defective items $=28$

Let $A$ denote event of selecting the non defective items.

$\Rightarrow n\left(A\right)=28$

$\Rightarrow P\left(A\right)=\frac{n\left(A\right)}{n\left(S\right)}=\frac{28}{35}=\frac{4}{5}$