Outliers, and choosing the best measure of center and spread

Answer Key - Grade 9 Math Worksheet - Building Confidence

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

1. 1.

   Bo recorded minutes spent reading after school. Q1 is 20 minutes and Q3 is 34 minutes. What is the upper fence, Q3 + 1.5 × IQR?

   55
2. 2.

   Esme counted jump rope skips in one minute. Q1 is 46 skips and Q3 is 61 skips. What is the upper fence, Q3 + 1.5 × IQR?

   83.5
3. 3.

   Jun measured bean plants in the class garden. Q1 is 28 cm and Q3 is 36 cm. What is the lower fence, Q1 − 1.5 × IQR?

   16
4. 4.

   Luz measured paper airplane flights (one took a nosedive). Q1 is 11 meters and Q3 is 16 meters. What is the lower fence, Q1 − 1.5 × IQR?

   3.5
5. 5.

   Milo recorded twelve piano practice times in minutes. Q1 is 22 and Q3 is 28, so the fences are 13 and 37. Which times are outliers?

   • Only 45
   • 18, 20, 31 and 45
   • No value is an outlier
6. 6.

   Noah measured twelve sunflower seedlings in cm. Q1 is 17 and Q3 is 22, so the fences are 9.5 and 29.5. Which heights are outliers?

   • Only 4
   • Only 26
   • No value is an outlier
   • 4, 15, 24 and 26
7. 7.

   Ren listed twelve quiz scores out of 20. Q1 is 13 and Q3 is 17, so the fences are 7 and 23. Which scores are outliers?

   • Only 20
   • 9, 12, 18 and 20
   • No value is an outlier
8. 8.

   Tala timed nine waits in the lunch line. The dots have a long tail to the right. The mean is 8 minutes and the median is 6 minutes. Which center describes a typical wait better?

   • The range, 15, because it covers every wait
   • The mean, 8, because it uses every wait and the tail is not a problem
   • The median, 6, because the long tail pulls the mean up
9. 9.

   Ari measured eight sunflowers in cm. The dots balance around the middle, with no outliers. The mean is 150 cm and the median is 151 cm. Which center describes a typical height better?

   • The mean, 150, because the dots balance with no outliers
   • The range, 14, because it covers every height
   • The median, 151, because an outlier pulls the mean, so the median is safer
10. 10.

    Bo timed nine bike rides in minutes. The dots balance around the middle, with no outliers. The mean is 27 minutes and the median is 28 minutes. Which center describes a typical ride better?

    • The median, 28, because an outlier pulls the mean
    • The range, 13, because it covers every ride
    • The mean, 27, because the dots balance with no outliers