#### Harry_the_cat

##### Senior Member

- Joined
- Mar 16, 2016

- Messages
- 1,884

For example, if \(\displaystyle \overline{X}=\overline{X_1} =\overline{X_2}=\overline{X_3}\), and \(\displaystyle sd =sd_1=sd_2=sd_3\)

I would say, intuitively, that mean time between any failure is \(\displaystyle \frac{1}{3}\overline{X}\). I want to say that std dev is \(\displaystyle \frac{1}{3} sd\) but I'm not convinced.

Any help appreciated.

And then I need to consider what if the means and std devs are not equal.