Because if your looking for probability, Its asking for the chance that it will be able to roll in a certain number so you have a 1/2 of it landing on one or the other side if it's a 2 sided coin or a 1/3 if you have a 3 sided triangle shaped dice.
First, we find how much fits into one inch of soil. We do this by multiplying 4 by 3. This equals 12. For every 12 cubic inches, the soil will be one inch deep. We divide 48 by 12 to see how many inches deep is it. This equals 4. The soil is 4 inches deep.
