Multiple choice

A bag contains $50$ coins and each coin is marked from $51$ to $100$. One coin is picked at random. The probability that the number of the coin is not a prime number, is ......

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

There are 50 coins numbered 51 to 100. The prime numbers in this range are 53, 59, 61, 67, 71, 73, 79, 83, 89, 97 (10 primes). The number of non-prime coins is 50 - 10 = 40. The probability is 40/50 = 4/5.

AI explanation

The total number of outcomes is 50. The prime numbers between 51 and 100 are 53, 59, 61, 67, 71, 73, 79, 83, 89, and 97, giving exactly 10 primes. Using the formula for probability, the chance of picking a prime is 10 out of 50, which equals 1/5. Therefore, the probability of picking a coin that is not a prime number is 1 minus 1/5, which equals 4/5.

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