GRAPHS AND STATISTICS

Probability Scale

Learn the reliable method for probability scale, then apply it to 11+ exam-style questions.

1 · WHAT YOU NEED TO KNOW

The idea

Probability Scale questions test how accurately you read, summarise and compare data.

Picture itCount favourable and possible outcomes
2 · THE METHOD

Follow these steps

  1. Read the title, labels, key and scale.
  2. Extract only the values needed.
  3. Apply the correct statistic or comparison and check the unit.
3 · WORKED EXAMPLES

See the method in action

Example 1

The spinner is fair. What is the probability of a marked sector on one spin? Give a fraction.

4 marked sectors out of 6
  1. Count 4 favourable sectors out of 6 equally likely sectors.
  2. The probability is 4/6 = 2/3.
Answer: 2/3
Example 2

The spinner is fair and spins are independent. What is the probability that both spins are unmarked? Give a fraction.

5 marked sectors out of 11
  1. There are 5 marked and 6 unmarked sectors out of 11.
  2. Multiply the fractions for the two independent outcomes: 36/121 = 36/121.
Answer: 36/121
4 · ELEVENSPRINT TIP

A useful shortcut

Read the scale before reading any bar, point or symbol.

5 · COMMON MISTAKES

Watch out for these

Counting symbols instead of using the key

Multiply the number of symbols, including partial symbols, by the key value.

6 · TRY IT YOURSELF

Three fresh questions

Ready to check the method? You will get three fresh, validated questions.