Sample means, margin of error and confidence intervals

Answer Key - Grade 11 Math Worksheet

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

1. 1.

   Bo's random sample of 80 students read a mean of 34 minutes a night. Using 2 standard deviations of the simulated dots as the margin, what is the upper end of the interval, in minutes?

   39
2. 2.

   Dot plot of 200 simulated sample results; the standard deviation of the dots is 0.15 hours. Esme's random sample of 60 students slept a mean of 7.2 hours. Using 2 standard deviations of the simulated dots as the margin, what is the lower end of the interval, in hours?

   6.9
3. 3.

   Jun's random sample of 150 students found 64% recycle at home. Using 2 standard deviations of the simulated dots as the margin, what is the lower end of the interval?

   56
4. 4.

   Dot plot of 200 simulated sample results; the standard deviation of the dots is 1.2 cm. Kira's random sample of 40 bean plants had a mean height of 22.5 cm. Using 2 standard deviations of the simulated dots as the margin, what is the upper end of the interval, in cm?

   24.9
5. 5.

   Luz plans a random sample of 400 students about reading time. Using 1/√n, what is the approximate margin of error, as a percent?

   5
6. 6.

   Pia reads that a district survey about bus rides will use a random sample of 1,600 students. Using 1/√n, what is the approximate margin of error, as a percent?

   2.5
7. 7.

   Ren reads that a state survey about sleep will use a random sample of 2,500 students. Using 1/√n, what is the approximate margin of error, as a percent?

   2
8. 8.

   In Tala's random sample of 120 students, the mean reading time was 6.4 hours a week, with a margin of error of 0.8 hours. Which statement is right?

   • Every student at the school reads between 5.6 and 7.2 hours a week, without exception.
   • The mean for all the school's students is likely between 4.8 and 8 hours.
   • The mean for all the school's students is likely between 5.6 and 7.2 hours.
   • The mean for all the school's students is exactly 6.4 hours.
9. 9.

   In Ari's random sample of 90 students, the mean sleep was 8.6 hours a night, with a margin of error of 0.3 hours. Which statement is right?

   • The mean for all the school's students is exactly 8.6 hours.
   • Every student at the school sleeps between 8.3 and 8.9 hours a night.
   • The mean for all the school's students is likely between 8.3 and 8.9 hours.
   • The mean for all the school's students is likely between 8 and 9.2 hours.
10. 10.

    In Bo's random sample of 150 students, the mean was 3.6 books read this month, with a margin of error of 0.4 books. Which statement is right?

    • The mean for all the school's students is likely between 2.8 and 4.4 books.
    • The mean for all the school's students is exactly 3.6 books.
    • Every student at the school reads between 3.2 and 4 books this month.
    • The mean for all the school's students is likely between 3.2 and 4 books.