Making Decisions with Probability

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Mathematics, Data Analysis and Probability

Grade 3- 5


Students learn about probability.


Facts to Know
Probability is a term used in mathematics to explain the chance that a future event will occur, or the likelihood of an outcome. Think to yourself. What is the likelihood of you eating ice cream today? Will it definitely happen? Will it definitely not happen? Will it perhaps happen? Probability helps us assign a numerical value to the likelihood of future events or outcomes. Some events, such as the sun rising each day, are certain. They have a probability of 100% or 1. Some events, such as a dog flying through the air, are impossible. They have a probability of 0% or 0.
Some events, such as catching a cold, may occur or may not occur. Depending on a number of outside influences, this particular event may be likely or unlikely. This likelihood may be assigned a number between 0% and 100% or between 0 and 1. For example, if you are usually pretty healthy, and you have been eating right all winter and dressing appropriately when you go outside, you may think you only have about a 10% chance of catching a cold. But if you have been around a lot of friends and family members who have had colds, or if you usually catch a cold every winter, you may think you have about an 80% chance of catching a cold.
For some events, which have only two outcomes, such as flipping a coin, the likelihood of either outcome is equally likely. This means there is an equal chance that these events will occur or not occur. They fall right in the middle and have a probability of 50%, .5, or 1/2.
In the case of the flipping coin, either heads or tails will appear. The likelihood of each outcome is equal.
Similarity, if the forecast calls for a 50% chance of rain, the meteorologist is telling you that there is an equally likely chance of rain and no rain.


  • Making Decisions with Probability
  • pencils

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