Confidence intervals from a sample, for averages and for percents

Answer Key - Grade 11 Math Worksheet

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

1. 1.

   Ari's random sample of 100 bus rides has an SD of 15 minutes. Using the 95% multiplier 1.96, what is the margin of error?

   2.94
2. 2.

   Bo's random sample of 64 backpacks has an SD of 20 ounces (one holds a whole library). Using the 95% multiplier 1.96, what is the margin of error?

   4.9
3. 3.

   Esme's random sample of 49 sunflowers has an SD of 14 centimeters. Using the 95% multiplier 1.96, what is the margin of error?

   3.92
4. 4.

   Jun's sample of 100 rides has mean 35 minutes and SD 10. What is the 95% interval?

   • 33.04 to 36.96 minutes
   • 25 to 45 minutes
   • 34 to 36 minutes
5. 5.

   Kira's sample of 64 backpacks has mean 120 ounces and SD 20. What is the 95% interval?

   • 100 to 140 ounces
   • 117.5 to 122.5 ounces
   • 115.1 to 124.9 ounces
6. 6.

   Luz's interval is 33.04 to 36.96 minutes. What was the sample mean?

   • 3.92 minutes
   • 1.96 minutes
   • 35 minutes
7. 7.

   Noah switches from 95% to 99% confidence with the same data. What happens to the interval?

   • It moves up
   • It gets wider
   • It gets narrower
8. 8.

   Pia wants half the margin of error. How many times bigger must the sample be?

   • 8 times
   • 4 times
   • 2 times
9. 9.

   Ren estimates the average minutes students spend on homework. Which standard error fits?

   • p ÷ n
   • s ÷ √n
   • √(p(1 − p) ÷ n)
10. 10.

    Tala estimates the percent of students who walk to school. Which standard error fits?

    • √(p(1 − p) ÷ n)
    • s ÷ n
    • s ÷ √n