What is the probability of rolling a number less than five on a standard number cube (6 sides)

Answer: 2/3

Here are the outcomes that are less than five = {1, 2, 3, 4}. There are A = 4 values here.

Here are all the outcomes possible: {1, 2, 3, 4, 5, 6}. There are B = 6 ways to roll a single number cube (aka dice).

Divide the two values: A/B = 4/6 = (2*2) / (2*3) = 2/3

The fraction 2/3 is approximately equal to 0.667 which converts to 66.7%