1.

Each two-digit number is written on a paper slip and these are all put in a box. What is the probability that the product of the digits of a number drawn is a prime number? What if three-digit numbers are used instead?

Answer»

Total two-digit numbers = 90 

Product of the digits of a number drawn is a prime number 12, 13, 15, 17, 21, 31, 51, 71. 

(1 is not a prime number)

Total number whose product of the digits drawn is a prime number = 8 

Probability of product of the digits drawn is a prime number = \(\frac{8}{90}=\frac{4}{45}\)

Total three-digit numbers = 900 

Product of the digits of a number drawn is a prime number 112, 113, 115, 117, 121, 131, 151, 171, 211, 311, 511, 711.

Total number whose product of the digits drawn is a prime number = 12

Probability of product of the digits drawn is a prime number = \(\frac{12}{900}=\frac{4}{300} =\frac{1}{75}\)



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