Students struggled with…

  • P(At least 1) problems when the probability was given in a story problem and not in a table.
  • Finding a conditional probability when given necessary probabilities in a story problem.


  • As soon as you read “at least 1” immediately write “1-P(None)”.  Instead of using a formula to find the probability of none, think about what you need to happen and list it as separate pieces.
    • For example, if a person has a 10% chance of being late to work, what is the probability that they are late at least 1 out of 5 days? To find the probability that they are late none of the days we need them to be on time (90%) for 5 days in a row (0.9 x 0.9 x 0.9 x 0.9 x 0.9). It may feel like overkill to write out all of these probabilities but it really does help with the conceptual understanding.
  • Have students rewrite the story problem in probability notation after they have read the problem.  This helps them to identify which formulas may be helpful.

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