**Lesson 7.1 – The Idea of a Confidence Interval**

**Interpret a confidence interval in context.****Determine the point estimate and margin of error from a confidence interval.****Use confidence intervals to make decisions.**

**Activity: Guess the Mystery Mean **

We’re switching gears in chapter 7 and will be investigating confidence intervals. The idea of a confidence interval is not totally new. It was foreshadowed a bit in chapter 3 when we discussed margin of error.

This activity will require a little more facilitating than others. You will need your chapter 6 test scores. Begin by quickly showing students all of the chapter 6 test scores. Each student should guess what they think the mean is. Write the guesses on the board. Then discuss as a class how we could make these estimates more accurate, hopefully they will say to take a random sample. Each group will take a random sample of 5 scores and find the mean. They can use Siri or a random number generator. After this, students need to create a margin of error. They could do this by using an approximation. For example, many students may say ±10%. Some students may remember from chapter 3 that we used margin of error = 2 × standard deviation so they could calculate that as well. Have the groups write their intervals on the board. Reveal the actual test average and circle all of the intervals that **captured** the true mean.

**Notes**

We use a sentence template for interpreting confidence intervals:

We are ___% confident that the interval from _____ to _____ captures the true mean/proportion of ________ (context).