Dave the jogger runs the same route every day (about 2.2 miles). On 18 consecutive days, he recorded the number of steps on his Fitbit. The results were

3,450 3,363 3,228 3,360 3,304 3,407 3,324 3,365 3,290

3,289 3,346 3,252 3,237 3,210 3,140 3,220 3,103 3,129

Click here for the Excel Data File

(a) Construct a 95% confidence interval for the true mean number of steps Dave takes on his run. (Round your answers to 2 decimal places.)

The 95% confidence interval is from

to

.

(b) What sample size would be needed to obtain an error of 20 steps with 95% confidence? (Enter your answer as a whole number (no decimals). Use a z-value taken to 3 decimal places in your calculations.)

Sample size