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2.3.3 Conditional probability (A-level only)

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Question 69

The continuous random variable T T\,T represents the operational lifespan, in days, of a bioluminescent underwater sensor. The probability density function of T T\,T is modeled by:

f(t)={c(25−t2)0≤t≤50otherwise f(t) = \begin{cases} c(25 - t^2) & 0 \le t \le 5 \\ 0 & \text{otherwise} \end{cases} f(t)={c(25−t2)0​0≤t≤5otherwise​

where c c\,c is a constant.

a.

Show that c=3250\displaystyle c = \frac{3}{250}c=2503​.

[2]
b.

Determine the cumulative distribution function F(t)F(t)F(t) for the interval 0≤t≤50 \le t \le 50≤t≤5.

[2]
c.

Calculate the probability that a randomly selected sensor remains operational for more than 3 days.

[2]
d.

Given that a sensor has already functioned for 3 days, determine the probability that it will last for at least 4 days in total.

[3]
e.

Five such sensors are deployed independently. Find the probability that exactly 2 of them remain operational for more than 3 days.

[3]

2.3.3 Conditional probability (A-level only) Questions

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