Date | May 2018 | Marks available | 3 | Reference code | 18M.2.SL.TZ1.T_5 |
Level | Standard Level | Paper | Paper 2 | Time zone | Time zone 1 |
Command term | Find | Question number | T_5 | Adapted from | N/A |
Question
Contestants in a TV gameshow try to get through three walls by passing through doors without falling into a trap. Contestants choose doors at random.
If they avoid a trap they progress to the next wall.
If a contestant falls into a trap they exit the game before the next contestant plays.
Contestants are not allowed to watch each other attempt the game.
The first wall has four doors with a trap behind one door.
Ayako is a contestant.
Natsuko is the second contestant.
The second wall has five doors with a trap behind two of the doors.
The third wall has six doors with a trap behind three of the doors.
The following diagram shows the branches of a probability tree diagram for a contestant in the game.
Write down the probability that Ayako avoids the trap in this wall.
Find the probability that only one of Ayako and Natsuko falls into a trap while attempting to pass through a door in the first wall.
Copy the probability tree diagram and write down the relevant probabilities along the branches.
A contestant is chosen at random. Find the probability that this contestant fell into a trap while attempting to pass through a door in the second wall.
A contestant is chosen at random. Find the probability that this contestant fell into a trap.
120 contestants attempted this game.
Find the expected number of contestants who fell into a trap while attempting to pass through a door in the third wall.
Markscheme
* This question is from an exam for a previous syllabus, and may contain minor differences in marking or structure.
(0.75, 75%) (A1)
[1 mark]
OR (M1)(M1)
Note: Award (M1) for their product seen, and (M1) for adding their two products or multiplying their product by 2.
(A1)(ft) (G3)
Note: Follow through from part (a), but only if the sum of their two fractions is 1.
[3 marks]
(A1)(ft)(A1)(A1)
Note: Award (A1) for each correct pair of branches. Follow through from part (a).
[3 marks]
(M1)
Note: Award (M1) for correct probabilities multiplied together.
(A1)(ft) (G2)
Note: Follow through from their tree diagram or part (a).
[2 marks]
OR (M1)(M1)
Note: Award (M1) for and (M1) for subtracting their correct probability from 1, or adding to their .
(A1)(ft) (G2)
Note: Follow through from their tree diagram.
[3 marks]
(M1)(M1)
Note: Award (M1) for and (M1) for multiplying by 120.
= 27 (A1)(ft) (G3)
Note: Follow through from their tree diagram or their from their calculation in part (d)(ii).
[3 marks]