Multiple choice

A box contains a number of marbles with serial number $18$ to $38$. A marble is picked at random. Find the probability that it is a multiple of $3$.

  1. $\dfrac {3}{5}$
  2. $\dfrac {7}{20}$
  3. $\dfrac {3}{4}$
  4. $\dfrac {1}{3}$
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D Correct answer
Explanation

Numbers 18 to 38: Total = 38 - 18 + 1 = 21. Multiples of 3: 18, 21, 24, 27, 30, 33, 36. Count = 7. Probability = 7 / 21 = 1/3.

AI explanation

The total number of marbles from 18 to 38 is 38 minus 18 plus 1, resulting in 21 marbles. The multiples of 3 in this range are 18, 21, 24, 27, 30, 33, 36, which totals 7 marbles. The probability is 7 favorable outcomes divided by 21 total outcomes. Simplifying the fraction 7 over 21 by dividing by 7 gives 1 over 3.

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