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4. Calculate Probability with a Formula
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In the previous video, you calculated the number of ways your teacher could roll each outcome with two dice, to determine your chances of receiving a longer lunch period.

In this video, you will: use the data you have collected to calculate the probability of each outcome, convert the result to a percentage, and round the decimal to the nearest tenth.

Finally, you will calculate the probability of rolling the number you chose at the beginning of the lesson.

Remember that probability tells you the likelihood that an event will happen.

In this example, it’s your chance of winning the longer lunch period based on the number you selected.

To calculate the probability, you'll need to know the number of possible combinations and the number of ways to roll each outcome.

First, find the number of possible combinations.

There are six ways to roll the orange die and six ways to roll the purple die.

Multiply the ways to roll each die to get the total number of possible combinations.

Check your work by highlighting the range in the chart...

And selecting Count from the dropdown menu.

Now that you’ve determined the number of possible combinations, find the likelihood of rolling each number.

To calculate probability, divide the number of ways to roll by the number of possible combinations.

Enter a formula in the first cell of the Probability column.

Begin with an equals sign...

Then, add the cell reference for the number of ways to roll a two.

Type a forward slash...

And the total number of possible outcomes.

Press enter to complete the formula.

Great!

You calculated the probability of rolling a 2.

Drag the formula to the rest of the cells to calculate the probability of rolling the other numbers.

You could leave your probability calculation as a decimal, but it’s difficult to interpret.

Probability is often expressed as a ratio, such as a one in four chance, or as a percentage, like a 25 percent chance.

In general, fractions or percentages are easier to understand than very small decimals.

To convert decimals into percentages, select the data in the probability column....

And change the number format.

The numbers are now expressed as a percent to the hundredths place.

Round the percentages to the tenths place.

Nice work!

You’ve now calculated the probability of each number being rolled as a percentage.

Remember the number you picked in the first video?

Highlight your chances of earning the longer lunch in your spreadsheet.

Now that you calculated the probability of rolling each number, consider whether you would you pick a different number.

Remember that probability doesn’t guarantee a specific outcome -- each combination still has a chance.

But probability does tell you which combination is most likely to be rolled by your teacher Now, it’s your turn: Determine the total possible combinations using multiplication, Calculate the probability of each outcome using division, and copy the formula into the rest of the column.

Convert the results to percentages, Round the numbers to the tenths place, And calculate the probability that the number you chose will be the one your teacher rolls.

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Instructions
  1. Determine the total possible combinations using multiplication.
  2. Calculate the probability of each outcome using division, and copy the formula into the rest of the column.
  3. Convert the results to percentages.
  4. Round the numbers to the tenths place.
  5. Calculate the probability that the number you chose will be the one your teacher rolls.