Representing a Quantitative Variable with Graphs
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AP Statistics › Representing a Quantitative Variable with Graphs
A delivery company recorded the number of packages delivered per route for 52 routes on a particular day, using the company’s route logs. The dotplot below summarizes the distribution.
Dotplot (packages per route):
60 | •
65 | ••
70 | •••
75 | ••••
80 | •••••
85 | ••••••
90 | •••••••
95 | ••••••
100| •••••
105| ••••
110| •••
115| ••
120| •
Which feature of the distribution is most evident?
A roughly symmetric distribution with a single peak around 90 packages
A strong left skew with a long tail toward low package counts
A uniform distribution from 60 to 120 packages
A bimodal distribution with peaks near 70 and 110 packages
A strong right skew with a long tail toward high package counts
Explanation
This question assesses interpreting dotplots for quantitative data like packages per route. The dotplot builds to a peak at 90 packages (7 routes), with symmetric decreases to both lower and higher values, showing a roughly symmetric, unimodal distribution centered around 90. The shape is bell-like without skew or gaps. Choice D could distract by suggesting bimodality, but there's only one peak, not two distinct ones. A mini-lesson: symmetric distributions often have mean ≈ median; always describe shape, center, spread (e.g., from 60 to 120), and any unusual features to understand the data's central tendency and variability.
A librarian recorded the number of books checked out by each of 55 patrons on a Saturday, using the library’s checkout system. The dotplot below shows the distribution.
Dotplot (books checked out):
0 | ••••••••••••••••
1 | •••••••••••
2 | •••••••
3 | ••••
4 | •••
5 | ••
6 | •
7 | •
8 |
9 |
10| •
Which feature of the distribution is most evident?
A uniform distribution from 0 to 10 books
A strong left skew with a long tail toward 0 books
A bimodal distribution with peaks at 0 and 10 books
A strong right skew with a long tail toward larger numbers of books
A symmetric distribution with a center near 3 books
Explanation
This question tests describing distributions from dotplots for quantitative data like books checked out. The dotplot reveals a high frequency at 0 books (16 patrons), with frequencies decreasing as the number increases, but a long tail extending to 10 books, creating a strong right skew. Most data points are clustered at lower values, with fewer high values stretching the tail. Choice B could mislead by suggesting left skew, but the tail is toward higher numbers, not lower. When analyzing distributions, note the shape (e.g., right-skewed means tail to the right), center (pulled toward the tail in skewed data), spread, and any peaks or gaps to understand the variable's behavior.
In a study of 50 randomly selected customers at a coffee shop, a manager recorded the number of minutes each customer waited from ordering to receiving a drink during the morning rush. The dotplot shows the distribution of wait times (in minutes). Which feature of the distribution is most evident?
The distribution shows a uniform pattern with roughly equal frequency at each minute.
The distribution is right-skewed with a possible high outlier around 12 minutes.
The distribution is approximately symmetric with no unusual observations.
The distribution is bimodal with two clearly separated clusters of equal size.
The distribution is strongly left-skewed with a long tail toward smaller wait times.
Explanation
This question tests your ability to describe the shape of a distribution from a dotplot. Looking at the dotplot of wait times, we can see that most customers waited between 2-6 minutes, with the frequency decreasing as wait times increase. There appears to be one or two customers who waited around 12 minutes, which stands out from the main cluster. This creates a distribution that has a longer tail extending to the right (toward higher values), which is the definition of right-skewed. The value around 12 minutes could be considered a high outlier since it's separated from the main body of data. When describing distributions, always look for the overall shape (symmetric, skewed, uniform), the number of peaks (unimodal, bimodal), and any unusual observations (outliers).
A meteorologist recorded daily rainfall amounts (in inches) for 45 days in a spring season at one weather station using a standard rain gauge. The dotplot below shows the distribution.
Dotplot (rainfall in inches):
0.0 | •••••••••••••••••••
0.1 | •••••••••
0.2 | •••••
0.3 | •••
0.4 | ••
0.5 | •
0.6 | •
0.7 |
0.8 |
0.9 |
1.0 | •
Which feature of the distribution is most evident?
A uniform distribution from 0.0 to 1.0 inches
A bimodal distribution with peaks at 0.0 and 1.0 inches of equal height
A strong left skew, with many high-rainfall days and a tail toward 0
A symmetric distribution centered around 0.5 inches
A strong right skew, with many low-rainfall days and a tail toward higher amounts
Explanation
This question involves identifying features in dotplots of quantitative data like rainfall amounts. The dotplot shows a high stack at 0.0 inches (19 days), decreasing frequencies toward higher amounts, with a tail extending to 1.0 inches, indicating strong right skew. Most days have little to no rain, with infrequent higher rainfall days. Choice B distracts by suggesting left skew, but the long tail is to the right, toward higher values. Key lesson: right-skewed distributions often occur with non-negative variables like rainfall; describe shape, center (low due to skew), spread, and peaks to highlight common versus rare events.
An online retailer recorded the number of items per order for 80 randomly selected orders placed on one day (from the full set of that day’s orders). The dotplot below shows the distribution.
Dotplot (items per order):
1 | ••••••••••••••••••••••••••
2 | •••••••••••••••••
3 | ••••••••••
4 | ••••••
5 | ••••
6 | •••
7 | ••
8 | •
9 | •
10| •
Which feature of the distribution is most evident?
A strong left skew, with most orders large and a tail to smaller orders
A symmetric distribution with center around 5 items
A uniform distribution from 1 to 10 items
A clear bimodal distribution with peaks at 1 and 10 items
A strong right skew, with most orders small and a tail to larger orders
Explanation
This question focuses on describing dotplots for quantitative data such as items per order. The dotplot has the highest frequency at 1 item (26 orders), with frequencies steadily decreasing toward higher numbers, forming a long tail to the right and strong right skew. Most orders are small, with rare larger ones extending the distribution. Choice C might mislead by claiming left skew, but the tail is to higher values, not lower. A mini-lesson: for skewed distributions, the mean is pulled toward the tail compared to the median; always describe shape, center (e.g., median for skew), spread, and any clusters to interpret the data meaningfully.
A wildlife biologist measured the lengths (in centimeters) of 60 fish captured from a lake using the same measuring board, then released them. The dotplot shows the distribution of fish lengths. Which feature of the distribution is most evident?
The distribution is strongly left-skewed with a tail toward smaller lengths.
The distribution is symmetric with no clear peak.
The distribution is approximately uniform across the entire range.
The distribution is bimodal, suggesting two common length groups.
The distribution is strongly right-skewed with a single high outlier.
Explanation
This question tests your ability to recognize a bimodal distribution in a dotplot. Looking at the fish length data, we can see two distinct clusters of dots: one group centered around 15-20 cm and another group centered around 35-40 cm, with relatively few fish in between. This creates two clear peaks or modes in the distribution, making it bimodal. This pattern often suggests two different populations or groups within the data - perhaps two different species of fish or fish at different life stages. Option C incorrectly identifies this as right-skewed with an outlier, but the second cluster is too substantial to be considered outliers. When examining distributions, bimodal patterns indicate that the data may come from two distinct groups that should potentially be analyzed separately.
A teacher recorded the quiz scores (out of 10 points) for 40 students in one class, grading each quiz with the same rubric. The dotplot shows the distribution of scores.
Which feature of the distribution is most evident?
The distribution is approximately symmetric and centered near 7
The distribution has an outlier above 12 points
The distribution is strongly skewed right because most scores are high
The distribution is bimodal with peaks near 3 and 9
The distribution is strongly skewed left because most scores are high
Explanation
This question tests your understanding of skewness in the context of quiz scores. Looking at the dotplot, you can see that most students scored high on the quiz (dots clustered on the right side near scores of 8, 9, and 10), with fewer students receiving lower scores that trail off toward the left. This creates a distribution where the tail extends toward the lower values, which defines a left-skewed distribution. Choice B correctly identifies this as strongly skewed left because most scores are high. The key insight is that skewness is named for the direction of the tail, not where most of the data is located - when most values are high and the tail points toward low values, the distribution is skewed left. This pattern often occurs with relatively easy assessments where most students perform well.
A librarian recorded the number of books checked out by each of 35 patrons on a Saturday, using the library’s checkout system totals per patron. The dotplot below shows the distribution of books checked out. Which feature of the distribution is most evident?
Skewed right with a few patrons checking out many more books than most
Approximately symmetric centered near 10 books
Skewed left with a few patrons checking out unusually few books
Bimodal with two peaks at low and high checkout counts
Uniform with approximately equal numbers of patrons at each count
Explanation
This question asks you to identify the shape of a distribution from a dotplot of library checkouts. The dotplot shows that most patrons check out a small number of books (clustered on the left), with the frequency decreasing as the number of books increases, and a few patrons checking out many more books than typical. This creates a long tail extending to the right (toward higher book counts), which is the defining characteristic of a right-skewed distribution. Choice C (skewed left) would show the opposite pattern with most data on the right. Right-skewed distributions are common for count data like library checkouts because while most people have moderate usage, a few heavy users create the long right tail. Remember that skewness is always named for the direction of the tail, not where the bulk of the data sits.
A school nurse recorded the number of minutes 60 students spent on a treadmill during a fitness screening, rounding to the nearest minute. The dotplot below shows the distribution of treadmill times (minutes) for these students. Which feature of the distribution is most evident?
Approximately symmetric with a single peak near the center
Skewed left (longer tail toward smaller times)
Bimodal with two clear clusters separated by a gap
Skewed right (longer tail toward larger times)
Uniform with roughly equal counts at each time value
Explanation
This question tests your ability to identify the shape of a distribution from a dotplot. Looking at the dotplot of treadmill times, we can see that most students have times clustered on the left side (shorter times), with the frequency gradually decreasing as we move toward longer times on the right. The distribution has a long tail extending toward the higher values (longer treadmill times), which is the defining characteristic of a right-skewed distribution. Choice A (symmetric) is incorrect because the data clearly has more values on one side than the other. When describing distributions, remember that skewness is named for the direction of the tail: right-skewed means the tail points right toward larger values, while left-skewed means the tail points left toward smaller values.
A teacher recorded quiz scores (out of 20) for 30 students in one class. Scores were read directly from the graded quizzes. The dotplot below shows the distribution of quiz scores. Which feature of the distribution is most evident?
Bimodal with two separated clusters of scores
Skewed left because many scores are near 20 with a tail toward low scores
Skewed right because a few students scored unusually high
Uniform with roughly equal counts for each score
No apparent pattern because the scores are random noise
Explanation
This question asks you to identify the distribution shape from a dotplot of quiz scores. Looking at the dotplot, we can see that most scores are concentrated near the maximum score of 20, with the frequency decreasing as scores get lower, creating a tail that extends toward the left (lower scores). This pattern indicates a left-skewed distribution - the bulk of the data is on the right (high scores) with a tail pointing left toward lower values. Choice A (skewed right) would show the opposite pattern. Left-skewed distributions in test scores often occur when the assessment is relatively easy for most students, causing scores to bunch up near the maximum. When identifying skewness, always look for the direction of the tail: left-skewed means the tail points toward smaller values on the left.