Question

5 defective glasses are accidentally mixed with 20 good ones. The good glasses and the defective ones look the same from the outside. If a glass is chosen at random, what is the probability that the chosen glass is good?

• A. $\frac{3}{8}$
• B. $\frac{4}{5}$
• C. $\frac{3}{5}$
• D. $\frac{2}{5}$

Answer 1

The correct option is B

$\frac{4}{5}$

Given, total number of glasses $=25(20+5)$
⇒ Total number of outcomes $=25$

Let $E$ be the event of getting good glass.

Number of good ones $=20$
⇒ Number of favourable outcomes $=20$

$\text{Probability P(E)}=\frac{\text{Number of outcomes favourable to E}}{\text{Number of all possible outcomes of the experiment}}$
$=\frac{20}{25}=\frac{4}{5}$
$\therefore$ The probability of getting a good glass is $\frac{4}{5}$.