Interval and conditional probabilities from a density
The continuous random variable X has density f given by the rules below
\[f(x)=\frac{1}{64}\,x^{3}\quad(0\le x\le 4)\]
\[f(x)=0\quad\text{outside }[0,4]\]
The event is \(\frac{4}{5}<X<\frac{8}{5}\)