Edexcel S2 2013 January — Question 5

Exam BoardEdexcel
ModuleS2 (Statistics 2)
Year2013
SessionJanuary
TopicCumulative distribution functions
TypeVerify CDF properties

5. The continuous random variable \(T\) is used to model the number of days, \(t\), a mosquito survives after hatching. The probability that the mosquito survives for more than \(t\) days is $$\frac { 225 } { ( t + 15 ) ^ { 2 } } , \quad t \geqslant 0$$
  1. Show that the cumulative distribution function of \(T\) is given by $$\mathrm { F } ( t ) = \begin{cases} 1 - \frac { 225 } { ( t + 15 ) ^ { 2 } } & t \geqslant 0
    0 & \text { otherwise } \end{cases}$$
  2. Find the probability that a randomly selected mosquito will die within 3 days of hatching.
  3. Given that a mosquito survives for 3 days, find the probability that it will survive for at least 5 more days. A large number of mosquitoes hatch on the same day.
  4. Find the number of days after which only \(10 \%\) of these mosquitoes are expected to survive.