Spread: Range & IQR

Range

Range is the simplest measure of spread: the largest value minus the smallest value. It's quick, but a single extreme value can stretch it a lot.

When you study range, slow down and write one example in your notebook without looking at the screen. That active step is what turns reading into learning.

Interquartile range (IQR)

IQR measures the spread of the middle 50% of the data. Because it ignores the extreme high and low values, it is less affected by outliers than the range.

When you study interquartile range (iqr), slow down and write one example in your notebook without looking at the screen. That active step is what turns reading into learning.

Why this matters

Spread: Range & IQR shows up constantly in two ways to measure how spread out a data set is. It also connects to what you will see on homework, quizzes, and the next unit in this grade.

Teachers often move fast in class. This page is here so you can pause, re-read, and practice until the idea feels familiar, not just until you have memorized a rule for one day.

Common mistakes to avoid

Rushing to the answer without writing steps. Middle-school math rewards clear work, and you catch errors earlier when steps are visible.

Mixing up similar ideas from the same topic. If two terms feel alike, make a two-column note: what is the same, what is different, and one example of each.

Key ideas from this lesson

1. Range
2. Interquartile range (IQR)