1MA0 Foundation November 2016 Paper 1 Q20
20 The diagram shows a security lock.
| A | B | C |
| 1 | 2 | 3 |
You have to enter the correct code to open the lock.
The correct code is B3
Dan does not know the code.
He enters at random one of the letters.
He then enters at random one of the numbers.
Work out the probability that Dan enters the correct code. (3)
| Working | Answer | Mark | Notes |
|---|---|---|---|
| (A, 1), (A, 2), (A, 3) (B, 1), (B, 2), (B, 3) (C, 1), (C, 2), (C, 3) | \(\frac{1}{9}\) | 3 | M1 for any 3 combinations with no incorrect combinations or for \(3 \times 3\) A1 for all 9 combinations with no duplicates or extras or for 9 B1 (dep on M1) for \(\dfrac{1}{\text{``}9\text{''}}\) Alternative scheme B1 for \(\frac{1}{3}\) seen M1 for \(\frac{1}{3} \times \frac{1}{3}\) A1 for \(\frac{1}{9}\) oe |