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Grade 7 · Data · Dependent Events and Probability

Track Changing Probabilities

Events become dependent when the first outcome changes the sample space for the second.

The big idea

Ask whether the first event changes what remains

Drawing a red tile and replacing it leaves the next probability unchanged. Keeping it out changes both the total tiles and the number of red tiles remaining.

Work it through

Draw two red tiles from 3 red and 2 blue without replacement

  1. 1. First draw: P(red) = 3/5.
  2. 2. After a red is removed, 2 red remain among 4 tiles.
  3. 3. Second draw: P(red) = 2/4.
  4. 4. Multiply along the tree branch: 3/5 × 2/4 = 3/10.