Andy has 4 red socks and 8 black socks in his drawer. He takes 2 socks at random from his drawer.

Mark scheme

Marking points from the official mark scheme (May/June 2018). The mark or mark type is shown in brackets.

1. [M1] Multiply 2 probs together and summing two 2-factor probs, unsimplified, condone replacement
2. [A1] Correct answer
3. [M1] Multiply 2 probs together and subtracting two 2-factor probs from 1, unsimplified, condone replacement
4. [A1] Correct answer
5. [M1] Multiply 2 combs together and dividing by a combination
6. [A1] Correct answer
7. [B1] Prob distribution table drawn, top row correct, condone additional values with p = 0 stated
8. [B1] P(0) or P(2) correct to 3sf (need not be in table)
9. [B1] All probs correct to 3sf, condone P(0) and P(2) swapped if correct
10. [B1ft] ft their table if 0, 1, 2 only, 0 < p < 1