Higher November 2024 Paper 3 Q21
21 A bag contains 25 discs.
11 are red, 9 are blue and 5 are yellow.
Ashley picks three of the discs at random without replacement.
Ashley’s first disc is red.
Work out the probability that all three discs are different colours. [3 marks]
| Answer | Mark | Comments |
|---|---|---|
| \(\dfrac{9}{24}\) or \(\dfrac{5}{24}\) | M1 | oe eg 0.375 or 0.208(3…) may be seen on a diagram or embedded in a calculation |
\(\dfrac{9}{24} \times \dfrac{5}{23}\ (\times 2)\) | M1dep | oe eg \(\dfrac{15}{184}\ (\times 2)\) or 0.08(15…) \((\times 2)\) |
| \(\dfrac{90}{552}\) or \(\dfrac{15}{92}\) or 0.163(0…) | A1 | oe fraction, decimal or percentage accept 0.16 with M2 awarded |
Additional guidance
| Ignore incorrect conversion if correct answer seen | |
| A correct embedded value seen eg \(\dfrac{11}{25} \times \dfrac{9}{24} \times \dfrac{5}{23}\) or \(\dfrac{11}{25} \times \dfrac{5}{24} \times \dfrac{9}{23}\) | M1M0A0 |
| \(\dfrac{9}{24} \times \dfrac{5}{23} \times \dfrac{5}{24} \times \dfrac{9}{23}\) | M1M0A0 |