Question

One of the factors of 34 is chosen at random. What is the probability that the factor is itself a two digit number?

Answer 1

A factor of 30 is chosen at random. What is the probability, as a decimal, that it is a 2-digit number?

The positive whole-number factors of 30 are:

1, 2, 3, 5, 6, 10, 15 and 30.

So, there are 8 of them. Of these, 3 have two digits. Writing each factor on a slip of paper, then putting the slips into a hat, and finally choosing one without looking, get that

P(factor of 30 chosen is a 2-digit number) = number of two-digit factors ÷ number of factors

=38=3×.125=.375