EXAMPLE 12 Finding

Find the value of that will produce a 95% confidence interval for if the sample size is .

Solution

  • Step 1 We go across the row labeled “Confidence level” in the table (Figure 16) until we see the 95% confidence level. Our is somewhere in this column.
  • Step 2 The degrees of freedom are . We go down the column until we see 19 on the left. The number in that row is our , 2.093.

Note: For the newer TI-84s

  1. Press 2nd DISTR and select 4:invT.
  2. Enter the area to the left of the value, then comma, then .
  3. Press ENTER.

451

For example, invT(0.975,19) gives 2.093024022. The TI-83 does not have this function.

image
Figure 8.16: FIGURE 16 Use the confidence level and the degrees of freedom to find .

NOW YOU CAN DO

Exercises 5–8.