My question is - If the life span of electric component distributes uniformly During the year, and in one device there's $3$ electronic components that are parallel to each other. What is the expected value of the device (in years)?
So If the components are parallel, that means that if one is broken, than all the device will not work. Meaning, the life span is the the life span of one electronic component? So I can say that the expected value of the device is $1$ year or am I missing something here?
This is false.
What you said is referred to devices connected in series (in a row).
If the devices are parallel, the system will work until the latest is working.
So the life of the system is equivalent to the $max(x)$
Now, you know that $f_X(x)=\mathbb{1}_{[0;1]}(x)$ and also $f_Z(z)=3z^2\mathbb{1}_{[0;1]}(z)$
Thus
$$\mathbb{E}[Z]=\int_0^1 3z^3 dz=\frac{3}{4}$$