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### Course: 8th grade (Illustrative Mathematics)>Unit 6

Lesson 7: Lesson 7: Observing more patterns in scatter plots

# Clusters in scatter plots

Learn what a cluster in a scatter plot is!

## What are clusters in scatter plots?

Sometimes the data points in a scatter plot form distinct groups. These groups are called clusters.
Consider the scatter plot above, which shows nutritional information for $16$ brands of hot dogs in $1986$. (Each point represents a brand.) The points form two clusters, one on the left and another on the right.
The left cluster is of brands that tend to be $\text{low in calories and low in sodium}$.
The right cluster is of brands that tend to be $\text{high in calories and high in sodium}$.

## Practice problems

To better wrap our minds around the idea of clusters, let's try a couple of practice problems.

### Problem 1: Male and female fish

Adult male Lamprologus callipterus (a type of fish) are much bigger than their female counterparts. They weigh about $13$ times as much. Also, while females reach a length of $6$ centimeters, males reach a length of $15$ centimeters.
Which of the plots shown below might describe measurements of a group of adult Lamprologus callipterus?

### Problem 2: SAT test scores

Some high school students in the U.S. take a test called the SAT before applying to colleges. The scatter plot below shows what percent of each state's college-bound graduates participated in the SAT in $2009\phantom{\rule{0.167em}{0ex}}\text{-}\phantom{\rule{0.167em}{0ex}}2010$, along with that state's average score on the math section.
There is a cluster of states with $\text{lower participation}$, and a cluster of states with $\text{higher participation}$.
What is the best interpretation of these clusters?