JAMB 2011 · UTME · Q49

Probability

Find the probability that a number picked at random from the set $\{43, 44, 45, \ldots, 60\}$ is a prime number.

Worked solution (try it first)

From 43 to 60 inclusive there are $60 - 43 + 1 = 18$ numbers.
The primes are 43, 47, 53 and 59.
51 is $3 \times 17$ and 57 is $3 \times 19$ .
So the probability is $\frac{4}{18} = \frac29$ , option C.

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