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.

   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
3. 3.

   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
4. 4.

   Milo plans a random sample of 625 students about recycling. Using 1/√n, what is the approximate margin of error, as a percent?

   4
5. 5.

   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
6. 6.

   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
7. 7.

   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?

   • The mean for all the school's students is likely between 4.8 and 8 hours.
   • 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 exactly 6.4 hours.
   • The mean for all the school's students is likely between 5.6 and 7.2 hours.
8. 8.

   In Zee's random sample of 200 bus riders, the mean bus ride was 18 minutes, with a margin of error of 2.5 minutes. Which statement is right?

   • The mean for all the school's bus riders is exactly 18 minutes.
   • The mean for all the school's bus riders is likely between 15.5 and 20.5 minutes.
   • The mean for all the school's bus riders is likely between 13 and 23 minutes.
   • Every bus rider at the school rides between 15.5 and 20.5 minutes, without exception.
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 likely between 8 and 9.2 hours.
   • The mean for all the school's students is likely between 8.3 and 8.9 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 exactly 8.6 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?

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