GATE Electrical 2015 Set 1 | Question: 1

Question

A random variable $X$ has probability density function $f(x)$ as given below:

$ f(x)= \begin{cases}  a+bx &  \text{ for } 0 < x < 1 \\  0 & \text{otherwise} \end{cases}$

If the expected value $E[x] = 2/3$, then $Pr[x < 0.5]$ is __________.