Simple Probability

The probability scale

Probability runs from 0 (impossible) to 1 (certain). One-half means an event is just as likely to happen as not.

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

Calculating probability

For equally likely outcomes, probability = (number of favorable outcomes) ÷ (total number of outcomes).

When you study calculating probability, 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

Simple Probability shows up constantly in find how likely a single event is on a 0-to-1 scale. 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. The probability scale
2. Calculating probability