Confidence intervals from a sample, for averages and for percents

Answer Key - Grade 11 Math Worksheet - Building Confidence

Circle the best answer, or write your answer on the line.

1. 1.

   Ari times 36 random lunch lines; the sample SD is 12 seconds. What is the standard error of the mean?

   2
2. 2.

   Esme asks 64 random students their reading minutes; the sample SD is 8 minutes (one says 'all weekend'). What is the standard error of the mean?

   1

3. Read this first

   Multiplier table for confidence intervals (standard normal values)

   confidence level	multiplier z*
   90%	1.645
   95%	1.96
   99%	2.576

4. 3.

   Using the table, which multiplier does Jun use for a 95% interval?

   • 1.645
   • 1.96
   • 2.576
5. 4.

   Using the table, which level gives Kira the widest interval?

   • 95%
   • 99%
   • 90%
6. 5.

   Milo's interval is 42 ± 3 minutes. What is the 42?

   • The margin of error
   • The sample size
   • The sample mean
7. 6.

   Noah's interval is 42 ± 3 minutes. What are its two ends?

   • 39 and 42 minutes
   • 42 and 45 minutes
   • 39 and 45 minutes
8. 7.

   How does Pia get the margin of error?

   • Multiplier × standard error
   • Mean × sample size
   • SD ÷ mean
9. 8.

   Ren's 95% interval for mean sleep is 7.6 to 8.2 hours. What does it estimate?

   • The true mean for everyone
   • Each student's own sleep
   • The sample's largest value
10. 9.

    Why must Tala's sample be random for an interval to make sense?

    • So the mean is 0
    • So it fairly stands for the group
    • So the numbers come out whole and neat
11. 10.

    What does '95% confident' mean for Zee's method?

    • 95% of the students' own values lie inside it
    • The mean is 95
    • About 95% of such intervals catch the truth