Higher January 2019 Paper 2R Q15
15 Barney has a biased coin.
When the coin is thrown once, the probability that the coin will land heads is 0.3
Barney throws the coin 4 times.
(a) Work out the probability that the coin will land heads exactly 3 times. (3)
(b) Work out the probability that the coin will land heads at least once. (2)
| Scheme | Marks |
|---|---|
| 0.3³ × 0.7 | M1 |
| 4 × 0.3³ × 0.7 | M1 |
| 0.0756 | A1 |
| (3) |
Notes
M1: oe
M1: oe
A1: \(\dfrac{189}{2500}\) or 0.075 or 0.076
| Scheme | Marks |
|---|---|
| 1 – 0.7⁴ oe | M1 |
| 0.7599 | A1 |
| (2) | |
| (5 marks) |
Notes
M1: Fully correct method
A1: 0.759 – 0.7560 (as printed in the mark scheme; the upper limit is presumably 0.760)