Helping math teachers bring statistics to life
Learning Targets

Find and interpret conditional probabilities using twoway tables.

Use the conditional probability formula to calculate probabilities.

Determine whether two events are independent.
Quiz 5.3
Chapter 5  Day 8
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.
Remedies…

As soon as you read “at least 1” immediately write “1P(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 noneof 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.