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.

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

   • 3.92 minutes
   • 35 minutes
   • 1.96 minutes
5. 5.

   Milo surveys 400 people instead of 100. What happens to the interval?

   • It gets wider
   • It gets narrower
   • It stays the same
6. 6.

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

   • It gets narrower
   • It moves up
   • It gets wider
7. 7.

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

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

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

   • √(p(1 − p) ÷ n)
   • p ÷ n
   • s ÷ √n
9. 9.

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

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

    In Zee's random sample, 90 of 300 students have a pet. What is the sample proportion p?

    • 0.90
    • 0.30
    • 3.33