Higher June 2019 Paper 2 Q10
10 Mary travels to work by train every day.
The probability that her train will be late on any day is 0.15
(a) Complete the probability tree diagram for Thursday and Friday.
(b) Work out the probability that her train will be late on at least one of these two days. (3)
| Answer | Mark | Mark scheme |
|---|---|---|
| Diagram completed | M1 | for \(1 - 0.15\ (= 0.85)\) |
| A1 | fully correct diagram |
Additional guidance
0.85
0.15, 0.85, 0.15, 0.85
| Answer | Mark | Mark scheme |
|---|---|---|
| 0.2775 | M1 | for one correct product eg \(0.15 \times 0.15\ (= 0.0225)\) or \(0.15 \times 0.85\ (= 0.1275)\) or \(0.85 \times 0.85\ (= 0.7225)\) |
| M1 | for a complete method eg \(\text{``}0.0225\text{''} + 2 \times \text{``}0.1275\text{''}\) OR \(1 - \text{``}0.7225\text{''}\) oe | |
| A1 | oe, eg \(\dfrac{111}{400}\) |
Additional guidance
ft their diagram provided probabilities are less than 1