Date | May 2012 | Marks available | 2 | Reference code | 12M.2.hl.TZ2.5 |
Level | HL only | Paper | 2 | Time zone | TZ2 |
Command term | Find | Question number | 5 | Adapted from | N/A |
Question
The random variable X has the distribution Po(m)Po(m) .
Given that P(X=5)=P(X=3)+P(X=4)P(X=5)=P(X=3)+P(X=4), find
the value of m ;
P (X > 2) .
Markscheme
P(X=5)=P(X=3)+P(X=4)P(X=5)=P(X=3)+P(X=4)
e−mm55!=e−mm33!+e−mm44!e−mm55!=e−mm33!+e−mm44! M1(A1)
m2−5m−20=0m2−5m−20=0
⇒m=5+√1052=(7.62)⇒m=5+√1052=(7.62) A1
[3 marks]
P(X>2)=1−P(X⩽2) (M1)
=1−0.018...
=0.982 A1
[2 marks]
Examiners report
Again this proved to be a successful question for many candidates with a good proportion of wholly correct answers seen. It was good to see students making good use of the calculator.
Again this proved to be a successful question for many candidates with a good proportion of wholly correct answers seen. It was good to see students making good use of the calculator.