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