A fair spinner has sides numbered 1, 2, 2. Another fair spinner has sides numbered –2, 0, 1. Each spinner is spun. The number on the side on which a spinner comes to rest is noted. The random variable X is the sum of the numbers for the two spinners.

Mark scheme

Marking points from the official mark scheme (May/June 2021). The mark or mark type is shown in brackets.

1. B1 Table with correct X values and at least one probability Condone any additional X values if probability stated as 0.
2. B1 2 correct probabilities linked with correct outcomes, may not be in table.
3. B1 3 further correct probabilities linked with correct outcomes, may not be in table.
4. M1 E(X) may be implied by use in variance, accept unsimplified expression. FT their table if their 3 or more probabilities sum to 1 or 0.999
5. M1 Appropriate variance formula using their (E(X))² value. FT their table even if their 3 or more probabilities not summing to 1.
6. A1 Answers for E(X) and Var(X) must be identified