**Paper 2 Higher - Sample Assessment Q12**

**Answers**

12) A and B are two sets of traffic lights on a road.

The probability that a car is stopped by lights A is 0.4

If a car is stopped by lights A, then the probability that the car is

If a car is not stopped by lights A, then the probability that the car is

(a) Complete the probability tree diagram for this information

(2 marks)

The probability that a car is stopped by lights A is 0.4

If a car is stopped by lights A, then the probability that the car is

**not**stopped by lights B is 0.7If a car is not stopped by lights A, then the probability that the car is

**not**stopped by lights B is 0.2(a) Complete the probability tree diagram for this information

(2 marks)

Mark drove along this road.

He was stopped by just one of the sets of traffic lights.

(b) Is it more likely that he was stopped by lights A or by lights B?

You must show your working.

(2 marks)

(Total for Question 12 is 5 marks)

He was stopped by just one of the sets of traffic lights.

(b) Is it more likely that he was stopped by lights A or by lights B?

You must show your working.

(2 marks)

(Total for Question 12 is 5 marks)

**Answers**

Question |
Answer |
Notes |

12 a |
0.4,0.6 0.3,0.7,0.8,0.2 |
B1 - correctly placing probs for light A eg 0.4, 0.6 B1 - correctly placing probs for light B eg 0.3, 0.7, 0.8, 0.2 |

12 b |
B with correct probabilities |
P1 - (ft) eg 0.4 × 0.3 or 0.6 × 0.8 or 1−(0.28+0.12)P1 - both sets of correct probability calculations C1 - Correct interpretation of results with correct comparable results |