Question

The probability that a teacher will give an unannounced test during any class meeting is $\frac{1}{5}$. If a students is absent twice, the probability that he will miss at least one test is:

• A. $\frac{7}{25}$
• B. $\frac{9}{25}$
• C. $\frac{16}{25}$
• D. $\frac{24}{25}$

Answer 1

The correct option is B $\frac{9}{25}$

Probability of not annoucing a test$=1-\frac{1}{5}=\frac{4}{5}$

Probability that he will miss atleast one test

$=1-\left(\frac{4}{5}\right)\left(\frac{4}{5}\right)$

$1-\frac{16}{15}=\frac{25-16}{25}=\frac{2}{25}$