Independent solution

How to solve this Continuous Random Variables question

Setup

Setup

A continuous median m satisfies F(m) = 0.5. First locate the density segment in which the cumulative probability reaches one-half.

Pr(X0.5)=0.80(0.5)=0.40\Pr(X\le 0.5)=0.80(0.5)=0.40

Model

Model

Because 0.40 is below one-half, continue through the following segment, where the density is constant at 0.30.

F(m)=0.40+0.30(m0.5),0.5<m1.5F(m)=0.40+0.30(m-0.5),\qquad 0.5<m\le 1.5

Compute

Compute

Set the segment-specific cumulative distribution equal to one-half and solve.

0.40+0.30(m0.5)=0.500.40+0.30(m-0.5)=0.50
m0.5=0.100.30=13m-0.5=\frac{0.10}{0.30}=\frac{1}{3}
m=56=0.833333m=\frac{5}{6}=0.833333\ldots

Answer

Answer

The median lifetime rounds to 0.83 year.

m0.83 year(B)\boxed{m\approx 0.83\text{ year}\quad\text{(B)}}