| Date | May 2018 | Marks available | 3 | Reference code | 18M.2.hl.TZ1.4 |
| Level | HL only | Paper | 2 | Time zone | TZ1 |
| Command term | Find | Question number | 4 | Adapted from | N/A |
Question
The age, L, in years, of a wolf can be modelled by the normal distribution L ~ N(8, 5).
Find the probability that a wolf selected at random is at least 5 years old.
[2]
a.
Eight wolves are independently selected at random and their ages recorded.
Find the probability that more than six of these wolves are at least 5 years old.
[3]
b.
Markscheme
P(L ≥ 5) = 0.910 (M1)A1
[2 marks]
a.
X is the number of wolves found to be at least 5 years old recognising binomial distribution M1
X ~ B(8, 0.910…)
P(X > 6) = 1 − P(X ≤ 6) (M1)
= 0.843 A1
Note: Award M1A0 for finding P(X ≥ 6).
[3 marks]
b.
Examiners report
[N/A]
a.
[N/A]
b.
