# Describing subsets of sample spaces exercise | Probability and Statistics | Khan Academy | Summary and Q&A

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March 8, 2015
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Describing subsets of sample spaces exercise | Probability and Statistics | Khan Academy

## TL;DR

Analyzing sample spaces and probabilities using examples from Harry Potter and a game called "Fire-Water-Sponge."

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### Q: How is the probability of selecting a wand made of holly or unicorn hair calculated?

To calculate the probability, we count the number of outcomes that involve holly or unicorn hair and divide it by the total number of equally likely outcomes, which is 20. In this case, there are 8 outcomes with holly or unicorn hair, resulting in a probability of 8/20 or 40%.

### Q: What determines the subset of outcomes in "Fire-Water-Sponge" where the friend either wins or there is a tie?

The subset in this case consists of outcomes where the friend either wins or there is a tie. We exclude outcomes where the player wins. In the highlighted outcomes (1, 3, 4, 5, 7, and 8), the friend either wins or there is a tie, leading to the subset that satisfies this condition.

### Q: How many possible outcomes are there in "Fire-Water-Sponge"?

In "Fire-Water-Sponge," there are 9 possible outcomes since each player has 3 choices (fire, water, or sponge), resulting in a total of 3 * 3 = 9 possibilities.

### Q: What determines the subset of outcomes where there is not a tie in "Fire-Water-Sponge"?

The subset consists of outcomes where there is not a tie. Since ties occur when both players choose the same object (fire-fire, water-water, or sponge-sponge), we exclude these outcomes from the subset. This leaves us with outcomes where someone wins (outcome 1, 3, 4, 5, 7, or 8).

## Summary & Key Takeaways

• The video discusses how to describe sets and subsets of sample spaces using examples from Harry Potter and a game called "Fire-Water-Sponge."

• In the Harry Potter example, the video calculates the probability of selecting a wand made of holly or unicorn hair.

• In the "Fire-Water-Sponge" example, the video analyzes the subset of outcomes where the friend either wins or there is a tie.