Date | May 2016 | Marks available | 3 | Reference code | 16M.2.hl.TZ2.2 |
Level | HL only | Paper | 2 | Time zone | TZ2 |
Command term | Find | Question number | 2 | Adapted from | N/A |
Question
A random variable X is normally distributed with mean 3 and variance 22.
Find P(0⩽X⩽2).
Find P(|X|>1).
If P(X>c)=0.44, find the value of c.
Markscheme
P(0⩽X⩽2)=0.242 (M1)A1
[2 marks]
METHOD 1
P(|X|>1)=P(X<−1)+P(X>1) (M1)
=0.02275…+0.84134… (A1)
=0.864 A1
METHOD 2
P(|X|>1)=1−P(−1<X<1) (M1)
=1−0.13590… (A1)
=0.864 A1
[3 marks]
c=3.30 (M1)A1
[2 marks]
Examiners report
Part (a) was generally well done. In each question part, a number of candidates could have benefited from producing a labelled sketch of the situation.
Part (b) was not well done with many candidates not knowing what P(|X|>1) represents. In each question part, a number of candidates could have benefited from producing a labelled sketch of the situation.
In part (c), a number of candidates did not recognise that P(X>c)=1−P(X⩽c). In each question part, a number of candidates could have benefited from producing a labelled sketch of the situation.