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Probability of not rolling a number

Probability of not rolling a number on a single dice

This math skill teaches how to calculate the probability of not rolling a specific number on a single die. It explains the concept of inverting the probability of rolling that specific number to determine the probability of not rolling it.

Learn probability of not rolling a number

Teaching Transcript

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What is the chance, or probability, of not rolling a 2 on a single die?

Here's a interesting trick to use when calculating probability. We know that one way to calculate probability is desired outcomes, divided by the total outcomes. However, we can also invert the problem. The chance of not getting a roll, is 100%, or 1, minus the chance of actually getting that roll.

Let's use the inverting trick. The chance of not getting a 2, is 1 minuse the chance of getting a 2, so that's 1, minus 1 over 6

If we do the subtraction, that's a probability of 5 over 6.

Let's check the original way to make sure they line up. There are 5 ways to not roll a 2 with one roll of a die. And there are 6 ways that a single roll can land, so our probability is also 5 divided by 6

Skill Practice

Probability of not rolling a number on a single dice

Test your understanding of probability of not rolling a number by practicing it! Work through the below exercises to use it in practice.