Comparing Distributions of a Quantitative Variable

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AP Statistics › Comparing Distributions of a Quantitative Variable

Questions 1 - 10
1

A company compares delivery times (minutes) for two shipping options: Standard and Express. The side-by-side summaries below were computed from similar sample sizes.

Which comparison is supported?

StatisticStandardExpress
Min2818
$Q_1$4030
Median5542
$Q_3$7555
Max160120
Outliers notedseveral high values above 140none noted

Both options have about the same median, but Express has a larger range.

Express has a higher median and more high outliers than Standard.

Standard has a lower median but a larger IQR; both show high outliers.

Standard has a higher median and larger IQR; only Standard shows high outliers.

Express has a lower median and a larger IQR than Standard.

Explanation

This question examines comparing delivery time distributions with five-number summaries and outliers in AP Statistics. The Standard option has a higher median (55 vs. 42) and larger IQR (35 vs. 25), indicating longer typical times with more variability, plus several high outliers above 140 only in Standard. Express shows no outliers, suggesting more consistency. Choice C distracts by claiming Standard has a lower median, which contradicts the data. In distribution comparisons, evaluate center (median), spread (IQR), and outliers; here, Standard's outliers inflate its max and range. Mini-lesson: Outliers can indicate skewness or anomalies—plot them on boxplots; higher medians with larger IQRs often mean a group is slower but more unpredictable.

2

Two teachers compare quiz scores (out of 20) from their classes. The distributions are summarized below.

Which comparison is supported?

StatisticClass AClass B
Min68
$Q_1$1211
Median1515
$Q_3$1718
Max2020

Class B has a lower median and a smaller overall range than Class A.

Both classes have the same median; Class B has a slightly larger IQR.

Both classes have the same median; Class A has a larger IQR.

Class A has a higher median, but both classes have the same IQR.

Class B has a higher median and a larger IQR than Class A.

Explanation

This question tests comparing quiz score distributions via five-number summaries in AP Statistics. Both classes share a median of 15, showing similar typical scores, but Class B has a slightly larger IQR (7 vs. 5), indicating more variability in the middle 50%. The ranges are identical (14 for both), and mins/maxs are close. Choice A distracts by claiming Class B has a higher median, which is false. Comparing distributions involves assessing center (same medians here), spread (larger IQR for B suggests more dispersion), and shape (both seem symmetric). Mini-lesson: Compute IQR as $Q_3 - Q_1$ to quantify spread; equal medians don't imply identical distributions—check spreads and extremes for full insights.

3

A teacher compared quiz scores (out of 10) for two classes, Class 1 and Class 2. The distributions are summarized using counts in each score bin (same bin widths). Which comparison is supported by the display?

Counts by score bin:

  • 0–2: Class 1 = 1, Class 2 = 3
  • 3–5: Class 1 = 4, Class 2 = 7
  • 6–8: Class 1 = 10, Class 2 = 6
  • 9–10: Class 1 = 5, Class 2 = 4

Class 1 is more variable because it has fewer scores in the middle bin 6–8.

Class 2 has a higher center because it has more scores in 3–5 than Class 1.

The classes have the same center because both have students scoring 9–10.

Class 1 appears to have a higher center than Class 2, with Class 2 having more low scores.

Class 2 has a higher typical score because it has more students total.

Explanation

This question assesses comparing quiz score distributions between two classes using binned counts, focusing on center and shape. Class 1 has more scores in higher bins (10 in 6-8, 5 in 9-10) versus Class 2 (6 in 6-8, 4 in 9-10), suggesting Class 1's higher center, while Class 2 has more low scores (3 in 0-2, 7 in 3-5) indicating a left-skewed shape with lower typical scores. Both have 20 students, so counts directly compare; spreads are similar across bins. Choice C distracts by claiming Class 2 has higher center due to more in 3-5, overlooking the overall shift toward higher bins in Class 1. In distribution comparisons, estimate center from where data clusters, compare spreads by bin coverage, and note shapes like skewness; binned data helps visualize without individual values.

4

Two brands of batteries (Brand X and Brand Y) were tested for lifetime (hours) until failure. A side-by-side boxplot summary is given by five-number summaries below. Which comparison is supported by the display?

  • Brand X: min 6, $Q_1$ 10, median 14, $Q_3$ 18, max 22; no outliers
  • Brand Y: min 4, $Q_1$ 9, median 13, $Q_3$ 17, max 19; no outliers

Brand X has a slightly higher median lifetime than Brand Y, and the spreads (IQRs) are the same.

Brand Y has a larger range and therefore a higher center.

Brand Y has a higher median lifetime than Brand X, and Brand Y has a larger IQR.

Brand X and Brand Y have the same median because their IQRs overlap.

Brand X is more variable because it has a smaller range.

Explanation

This problem focuses on comparing battery lifetime distributions for Brand X and Brand Y using boxplots and five-number summaries. Brand X has a median of 14 hours, slightly higher than Y's 13, showing a marginally higher center, and both have identical IQRs of 8 hours (X: 18-10, Y: 17-9), indicating similar middle 50% spreads. The ranges are close (X: 16, Y: 15), with no outliers, supporting comparable variability. Choice A tempts by reversing the medians and claiming Y has larger IQR, possibly from miscalculating or swapping groups. Remember, in comparing quantitative distributions, prioritize center (median for skewed data), spread (IQR resists outliers), and note any unusual features like outliers; here, the slight difference in medians and equal IQRs are key.

5

A researcher compared commute times (minutes) for employees who drive versus employees who take public transit. Five-number summaries are shown below. Which comparison is supported by the display?

  • Drive: min 10, $Q_1$ 18, median 25, $Q_3$ 35, max 55; no outliers
  • Transit: min 15, $Q_1$ 25, median 40, $Q_3$ 55, max 90; no outliers

Driving has a higher median commute time than transit, and driving has a larger IQR.

Transit must have outliers because its maximum is 90.

The two groups have similar centers because their minimums are close.

Transit has a higher median commute time than driving, and transit has a larger IQR.

Driving is more variable because its maximum is smaller.

Explanation

Comparing commute time distributions for driving and transit users involves five-number summaries to evaluate center and variability. Transit's median is 40 minutes, higher than driving's 25, showing longer typical commutes, and transit's IQR of 30 (55-25) exceeds driving's 17 (35-18), indicating greater middle spread; transit's higher maximum (90 vs. 55) also suggests more variability. No outliers are noted, and shapes aren't detailed, but centers and spreads differ clearly. A distractor is choice A, which reverses the medians and IQRs, possibly from confusing group labels. Mini-lesson: for quantitative variables, compare centers (medians), spreads (IQR for robustness), and outliers; boxplots visually aid in seeing overlaps or shifts in distributions.

6

A city compared the ages (years) of cars in two neighborhoods: Neighborhood East and Neighborhood West. Five-number summaries are shown below. Which comparison is supported by the display?

  • East: min 1, $Q_1$ 3, median 6, $Q_3$ 9, max 14; no outliers
  • West: min 0, $Q_1$ 2, median 4, $Q_3$ 7, max 20; one high outlier at 20

East is more variable because it has no outliers.

East has a higher median car age than West, and West shows greater overall spread due to a high outlier.

The medians must be the same because the IQRs overlap.

West has a higher median car age than East, and West has a smaller range.

West has a smaller IQR than East because its maximum is larger.

Explanation

This question involves comparing car age distributions in two neighborhoods using five-number summaries to identify differences in center and spread. East has a higher median age of 6 years versus West's 4, indicating older typical cars, while West's high outlier at 20 years increases its overall spread (range 20-0=20) compared to East's (14-1=13). IQRs are similar (East: 9-3=6, West: 7-2=5), but the outlier affects West's total variability. Choice A distracts by reversing the medians and claiming West has smaller range, disregarding the outlier's extension. In comparing distributions, use median for center, IQR for consistent spread, and consider outliers separately as they can inflate range without representing typical variability.

7

An environmental club compares the weights (in pounds) of trash collected per volunteer during two events: a beach cleanup (Beach) and a park cleanup (Park). The side-by-side five-number summaries are shown.

Which comparison is supported?

StatisticBeachPark
Min21
$Q_1$86
Median1412
$Q_3$2016
Max3540

Beach has a higher median and a larger IQR than Park.

Park has a higher median and a larger IQR than Beach.

Park has a higher median, and Beach has a larger overall range.

Both events have the same median, but Park has a larger overall range.

Beach has a lower median, but Park has a smaller IQR.

Explanation

This question assesses comparing trash weight distributions with five-number summaries in AP Statistics. The Beach event has a higher median (14 vs. 12 lbs) and larger IQR (12 vs. 10 lbs), indicating more typical trash per volunteer with greater middle variability. Park has a larger range (39 vs. 33) due to its max. Choice B distracts by assigning higher median and IQR to Park, which is incorrect. Comparing distributions requires examining center (median for typical value), spread (IQR for consistency), and extremes; both seem right-skewed. Mini-lesson: Higher medians suggest overall shifts; larger IQRs mean more dispersion in core data—visualize with boxplots to see overlaps or differences.

8

Two brands of batteries are tested for how long they last (hours) in the same device. The results are summarized below.

Which comparison is supported?

StatisticBrand XBrand Y
Mean9.810.1
Median10.29.9
Shapeleft-skewedright-skewed
IQR1.41.4

Brand X and Brand Y have the same center because their IQRs are equal.

Brand X has a larger IQR, so it must have the larger mean.

Brand X is right-skewed and Brand Y is left-skewed, so Brand X must have a lower mean.

Brand Y has a higher mean and a higher median than Brand X.

Brand Y has a slightly higher mean, but Brand X has a higher median; the IQRs are equal.

Explanation

This question evaluates comparing battery life distributions using means, medians, shapes, and IQRs in AP Statistics. Brand Y has a slightly higher mean (10.1 vs. 9.8 hours) but lower median (9.9 vs. 10.2), with equal IQRs of 1.4, reflecting shape influences—Y is right-skewed, X left-skewed. Skewness explains why Y's mean exceeds its median, unlike X. Choice A distracts by claiming Y has both higher mean and median, ignoring the reversal. In comparisons, note how shape affects center measures; equal IQRs indicate similar variabilities. Mini-lesson: In skewed distributions, medians resist tail pulls unlike means—left-skew pulls mean below median, right-skew above; compare both for insights.

9

A principal compares the number of absences per student in a semester for 9th graders and 12th graders. The side-by-side summaries below come from random samples.

Which comparison is supported?

Statistic9th grade12th grade
Min00
$Q_1$11
Median32
$Q_3$64
Max2512
Outliers notedseveral high values above 15none noted

9th grade has a higher median and a larger IQR; only 9th grade shows high outliers.

Both grades have the same median, but 12th grade has more high outliers.

9th grade has a lower median, but 12th grade has a larger overall range.

Both grades have the same IQR, but 9th grade has a higher maximum.

12th grade has a higher median and a larger IQR than 9th grade.

Explanation

This question tests comparing absence distributions with five-number summaries and outliers in AP Statistics. The 9th grade has a higher median (3 vs. 2) and larger IQR (5 vs. 3), showing more typical absences with greater variability, plus several high outliers above 15 only in 9th. 12th has a smaller range (12 vs. 25). Choice A is a distractor, wrongly giving higher median and IQR to 12th. Comparing involves center (median), spread (IQR), and outliers; 9th appears more right-skewed due to outliers. Mini-lesson: Outliers can extend ranges—identify them using 1.5*IQR rule; higher medians with larger IQRs suggest a group has more issues overall.

10

A city compares daily water use (in gallons) for two types of households: those with low-flow showerheads (Low-flow) and those with standard showerheads (Standard). Summary measures are shown.

Which comparison is supported?

StatisticLow-flowStandard
Mean210230
Median205225
IQR6060
Range260240

Low-flow has a higher center (mean and median) and the same IQR as Standard.

Standard has a higher center (mean and median), and the IQRs are the same.

Low-flow has a lower median but a larger IQR than Standard.

Standard has a higher center, and Low-flow has a smaller range.

Both groups have the same center, but Standard has a larger IQR.

Explanation

This question focuses on comparing water use distributions using means, medians, IQRs, and ranges in AP Statistics. The Standard group has higher center measures (mean 230 vs. 210, median 225 vs. 205), suggesting greater typical usage, with identical IQRs of 60 indicating similar middle spreads. The ranges differ slightly (240 vs. 260), but this isn't emphasized in the supported comparison. Choice A is a distractor, incorrectly giving Low-flow the higher center. To compare distributions, use mean and median for center (noting skewness if they differ), IQR for spread resistant to outliers, and range for overall variability; here, both groups have comparable spreads. Mini-lesson: When means and medians align in direction, it supports consistent center differences; equal IQRs mean similar variability in the central data, regardless of extremes.

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