AI generatedProbabilityKey Stage 3

Calculating a theoretical probability

Calculating a theoretical probability.

  • Probability = favourable outcomes ÷ all outcomes when individual outcomes are equally likely.
  • A probability lies between 0 and 1; complementary probabilities sum to 1.
  • Experimental relative frequency estimates probability and can vary between samples.

Example 1

A bag contains 2 red counters and 6 blue counters. Each counter is equally likely to be selected. Find .

Count the favourable counters and divide by all counters.

Example 2

A bag contains 3 red counters and 6 blue counters. Each counter is equally likely to be selected. Find .

Count the favourable counters and divide by all counters.

Your turn

Question 1

A bag contains 4 red counters and 6 blue counters. Each counter is equally likely to be selected. Find .

Check answer
Count the favourable counters and divide by all counters.
Question 2

A bag contains 5 red counters and 6 blue counters. Each counter is equally likely to be selected. Find .

Check answer
Count the favourable counters and divide by all counters.
Question 3

A bag contains 6 red counters and 6 blue counters. Each counter is equally likely to be selected. Find .

Check answer
Count the favourable counters and divide by all counters.
Question 4

A bag contains 7 red counters and 6 blue counters. Each counter is equally likely to be selected. Find .

Check answer
Count the favourable counters and divide by all counters.
Question 5

A bag contains 8 red counters and 6 blue counters. Each counter is equally likely to be selected. Find .

Check answer
Count the favourable counters and divide by all counters.