Probability that a teacher will give an unannounced test during any class meeting is 1/5 . If a stud

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14.Probability

hard

The probability that a teacher will give an unannounced test during any class meeting is $1/5$. If a student is absent twice, then the probability that the student will miss at least one test is

A

$\frac{4}{5}$

B

$\frac{2}{5}$

C

$\frac{7}{5}$

D

$\frac{9}{{25}}$

Solution

(d) The probability that one test is held $ = 2 \times \frac{1}{5} \times \frac{4}{5} = \frac{8}{{25}}$

Probability that one test is held on both days $ = \frac{1}{5} \times \frac{1}{5} = \frac{1}{{25}}$

Thus the probability that the student misses at least one test $ = \frac{8}{{25}} + \frac{1}{{25}} = \frac{9}{{25}}.$

Standard 11

Mathematics

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