4400 Higher June 2009 Paper 4 Q14
14 A coin is biased so that when it is thrown, the probability that it will show Heads is \(\dfrac{3}{4}\)
The coin is thrown twice.
(a) Complete the probability tree diagram.
(b) Work out the probability that the coin shows Tails on both throws. (2)
| Scheme | Marks |
|---|---|
| \(\frac{1}{4}\) | B1 |
| binary tree structure | B1 |
| all probs & labels correct | B1 |
| (3) |
Notes
B1: P(tail) on 1st throw
| Scheme | Marks |
|---|---|
| “\(\frac{1}{4}\)” × “\(\frac{1}{4}\)” | M1 |
| \(\frac{1}{16}\) or 0.0625 | A1 |
| (2) | |
| (5 marks) |
Notes
M1: ft their 2 tail branches
A1: cao