A three-digit number has three different odd digits. What is the fraction of all such three-digit numbers that are divisible by three?

There are:  135  153  159  195  315  351  357  375  513  519  531  537  573  579  591  597  735  753  759  795  915  951  957  975  Total =  24 such numbers.

 

What fraction of all 3-digit numbers is 24? Is that what you mean? If so, then: 24 / 900=2 / 75