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.

   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
2. 2.

   Kira listed the class's spelling quiz scores out of 50. Q1 is 32 points and Q3 is 42 points. What is the lower fence, Q1 − 1.5 × IQR?

   17
3. 3.

   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
4. 4.

   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?

   • 18, 20, 31 and 45
   • Only 45
   • No value is an outlier
5. 5.

   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
   • 4, 15, 24 and 26
   • No value is an outlier
   • Only 26
6. 6.

   Pia timed twelve bus rides home in minutes. Q1 is 16 and Q3 is 21, so the fences are 8.5 and 28.5. Which rides are outliers?

   • Only 33
   • No value is an outlier
   • 3 and 33
   • 3, 14, 23 and 33
7. 7.

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

   Zee listed nine spelling scores out of 10. The dots have a long tail to the left. The mean is 8 and the median is 9. Which center describes a typical score better?

   • The median, 9, because the long tail pulls the mean down
   • The mean, 8, because it uses every score and the tail is not a problem
   • The range, 7, because it covers every score
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 range, 14, because it covers every height
   • The median, 151, because an outlier pulls the mean, so the median is safer
   • The mean, 150, because the dots balance with no outliers
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