Let XXX be a continuous random variable with PDF f(x)=18xf(x) = \frac{1}{8}xf(x)=81x for 0≤x≤40 \le x \le 40≤x≤4. What is E[X]E[X]E[X]?
83\frac{8}{3}38
163\frac{16}{3}316
222
444