Date | May 2017 | Marks available | 3 | Reference code | 17M.1.hl.TZ2.7 |
Level | HL only | Paper | 1 | Time zone | TZ2 |
Command term | Find | Question number | 7 | Adapted from | N/A |
Question
The random variable \(X\) has the Poisson distribution \({\text{Po}}(m)\). Given that \({\text{P}}(X > 0) = \frac{3}{4}\), find the value of \(m\) in the form \(\ln a\) where \(a\) is an integer.
The random variable \(Y\) has the Poisson distribution \({\text{Po}}(2m)\). Find \({\text{P}}(Y > 1)\) in the form \(\frac{{b - \ln c}}{c}\) where \(b\) and \(c\) are integers.
Markscheme
\({\text{P(}}X > 0) = 1 - {\text{P(}}X = 0)\) (M1)
\( \Rightarrow 1 - {{\text{e}}^{ - m}} = \frac{3}{4}\) or equivalent A1
\( \Rightarrow m = \ln 4\) A1
[3 marks]
\({\text{P}}(Y > 1) = 1 - {\text{P}}(Y = 0) - {\text{P}}(Y = 1)\) (M1)
\( = 1 - {{\text{e}}^{ - 2\ln 4}} - {{\text{e}}^{ - 2\ln 4}} \times 2\ln 4\) A1
recognition that \(2\ln 4 = \ln 16\) (A1)
\({\text{P}}(Y > 1) = \frac{{15 - \ln 16}}{{16}}\) A1
[4 marks]