There are 100 lettered tiles in a board game. you chose the following tiles without looking: d, g, k, a, i.
how many of the 100 tiles would you expect to be vowels?

40 tiles

Assuming the vowels and non-vowels are equal to the five picked, there would be 40 tiles that are vowels.

You have picked five different letters. 5% or 1/20 of 100. If two of those five were vowels, then if you consistently pick 2/5 vowels every time, a predicted 40 tiles will be vowels, 60 would not.