Simple probability worksheets

The probability of one event is how many ways it can happen over how many ways anything can. These free printable worksheets describe a bag of counters and ask for that chance as a fraction in its simplest form.

Kid stuck on one? You don’t just get the sheet.

Simple probability
Simple probability worksheet — One event, simplified fraction, free printable with answer key

The answer key prints on a separate page.

What's on this sheet

Two steps hide in every answer and only the second is arithmetic. First decide the whole — the total number of counters — then count the ones that count as a success, and write the second over the first. A child who counts four blue and eight red and writes 4/8 has used the reds as the whole instead of everything, and that wrong-denominator slip is the one that survives longest.

Why this sheet works

Answers simplify, so the sheet doubles as fraction practice: 4/12 is written 1/3, because a probability that is not reduced is usually not accepted. Because the answer is a fraction, these sheets stay on paper — the online pad marks a single number, and a fraction is two — while the count-prediction sheets are the part of probability that can be practiced on screen.

How this one works

One question from this sheet, worked through a step at a time.

3 red, 7 blue, 2 green — P(green)

3 + 7 + 2=12
3 + 7 + 2=12
green:2
3 + 7 + 2=12
green:2
3 + 7 + 2=12
=
  1. Count EVERYTHING first, before the ones being asked about: 3 + 7 + 2 = 12 altogether. That is the bottom of the fraction, and it is the half that gets swapped for the wrong number.
  2. Now the ones that count as a win: 2 green.
  3. Chance is the wins OVER the total — not over the rest. So it is 2 out of 12.
  4. And 2/12 can be written in bigger pieces: 1/6.