A number is chosen at random from 1 to 30. What is the probability that it is divisible by 3 or 5?

\frac{1}{15}

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\frac{7}{15}

Correct answerYour answer

\frac{1}{2}

Correct answerYour answer

\frac{8}{15}

Correct answerYour answer

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CorrectNot quiteAnswer B

Correct answer: B

Divisible by 3: 10; by 5: 6; by both, that is by 15: 2.
By the addition rule, $10 + 6 - 2 = 14$ , so the probability is $\frac{14}{30} = \frac{7}{15}$ .

Worth noting

$\frac{16}{30}$ counts 15 and 30 twice.

Ten questions from Probability, at your own pace.

Explanation