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How to Calculate Chance Probability

Chance probability reports the likelihood that a random event will occur based on the total number of outcomes and the number of those outcomes considered successful. The definition of a successful outcome depends on the situation. For example, if dealing cards from a deck, there are 52 total outcomes. If you want an ace, since there are only four aces in the deck, you have four successful outcomes. However, if you want a spade, there are 13 successful outcomes.

Calculator

Instructions

- 1
  Count the number of possible outcomes. For example, if you are being dealt a card and you win if the card is red, the total number of possible outcomes would be the number of cards in the deck, or 52.
- 2
  Count the number of successful possible outcomes. In this example, since you need a red card to win, 26 cards are red so you have 26 successful possible outcomes.
- 3
  Divide the number of successful possible outcomes by the number of possible outcomes. In this example, divide 26 by 52 to get 0.5.
- 4
  Multiply the result to find the probability expressed as a percentage. Completing the example, multiply 0.5 by 100 to get a 50 percent probability that a red card will be dealt.

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Biological Science Subjects in Middle Schools