# Math Help - Stats first year help

1. ## Stats first year help

Hello, i am preparing for my Statistics examination and would like to ask help with the questions i struggle.

Am i right with these two?

Would appreciate if You could help with any of these.

2. Originally Posted by fancynick
Hello, i am preparing for my Statistics examination and would like to ask help with the questions i struggle.

The pdf is:

$f(x)=\begin{cases}
\theta e^{-\theta x}& , x>0\\
0& , \text{otherwise}
\end{cases}$

and the sketch looks OK

CB

..

3. Originally Posted by fancynick

$\displaystyle E(x)=\int_{x=0}^{\infty} x\, \theta e^{-\theta x}\; dx$

so:

$\displaystyle E(x)=\left[-\dfrac{\left( \theta\,x+1\right) \,{e}^{-\theta\,x}}{\theta}\right]_{x=0}^{\infty}=\frac{1}{\theta}$

CB