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Grade 9 · Math · Algebra 1

9th grade Outliers, and choosing the best measure of center and spread worksheet

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Outliers, and choosing the best measure of center and spread

Grade 9 Math Worksheet - Challenge Me

NameDate

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

  1. Jun recorded twelve library visits in minutes. The values are not in order. How many of them are outliers by the 1.5 × IQR rule?

  2. Kira counted jump rope skips in a minute for twelve classmates. The values are not in order. How many of them are outliers by the 1.5 × IQR rule?

  3. Luz measured twelve sunflowers in cm. The values are not in order. How many of them are outliers by the 1.5 × IQR rule?

  4. Milo listed the pages in twelve library books. The values are not in order. How many of them are outliers by the 1.5 × IQR rule?

  5. Noah timed eight maze runs in minutes. The run of 39 minutes is an outlier. When it is removed, how much more does the mean drop than the median?

  6. Pia measured eight bean sprouts in mm. The sprout of 52 mm is an outlier. When it is removed, how much more does the mean drop than the median?

  7. Ren counted skips in 30 seconds for eight classmates (one rope tangled). The count of 7 skips is an outlier. When it is removed, how much more does the mean rise than the median?

  8. Tala recorded eight quiz scores out of 40. The score of 6 points is an outlier. When it is removed, how much more does the mean rise than the median?

  9. Ari measured bean plants from two windowsills, eight each, in cm. Group A has one outlier, 47. Which statement compares the two groups fairly?

    • B's typical height is taller (medians 26 and 24.5), and A is more spread out (ranges 27 and 14).
    • A's typical height is taller (medians 24.5 and 26), and B's middle half is less spread (IQRs 8 and 3).
    • B's typical height is taller (medians 26 and 24.5), and A's middle half is less spread (IQRs 3 and 8).
    • A's typical height is taller (means 26.75 and 26), and A's middle half is less spread (IQRs 3 and 8).
  10. Esme counted pages read in a day by two reading groups of eight. Group A has one outlier, 52. Which statement compares the two groups fairly?

    • A's typical count is higher (medians 20.5 and 21.5), and B's middle half is less spread (IQRs 9 and 4).
    • B's typical count is higher (medians 21.5 and 20.5), and A's middle half is less spread (IQRs 4 and 9).
    • B's typical count is higher (medians 21.5 and 20.5), and A is more spread out (ranges 38 and 16).
    • A's typical count is higher (means 23.375 and 20.625), and A's middle half is less spread (IQRs 4 and 9).
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9th grade Outliers, and choosing the best measure of center and spread worksheet – printable
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About this worksheet

Outliers, and choosing the best measure of center and spread. Every version has 10 questions, and the answer key prints on the second page.

What your child will learn

  • I can find the fences Q1 − 1.5 × IQR and Q3 + 1.5 × IQR and name the outliers.
  • I can say whether the mean or the median shows a typical value, from the shape of the dots.
  • I can compare two groups fairly when one of them has an outlier.

Standard: S-ID.A.2, S-ID.A.3

Words to know

quartiles (Q1, Q3): The middles of the lower half and the upper half of the ordered values.

IQR: Q3 − Q1: how wide the middle half of the dots is.

fence: The line 1.5 IQRs past Q1 or Q3. A dot past a fence is an outlier.

outlier: A value past a fence: far from the rest of the dots.

skewed, tail: Most dots bunch up, and a few stretch out to one side.

symmetric: The dots balance around the middle, about the same on each side.

standard deviation (SD): A spread measure built from gaps to the mean; topic 64 shows how to find it.

Common mistakes

Your child stepped one IQR past the box instead of 1.5 IQRs.

Your child measured the fence from the wrong end of the box.

Your child found how far past the box the fence is, but stopped before placing the fence.

What to say

Ask: what do we multiply the IQR by before we add or subtract it?

Ask: which end of the box is closer to the high values, and which to the low ones?

Ask: where does that distance start?

Questions parents ask

What is the most common mistake with outliers, and choosing the best measure of center and spread?

Your child stepped one IQR past the box instead of 1.5 IQRs.

How can I help my child with outliers, and choosing the best measure of center and spread?

Ask: what do we multiply the IQR by before we add or subtract it?

Are these 9th grade math worksheets free to print?

Yes. All 6 printable versions at each level are free to print, with the answer key, and no account is needed.

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