Math Help - standard normal formula

Hi;
I know the formula is Z = (X - mean)/standard deviation,What I don't know
is how do I know when I convert a normal distribution into z
which is written as X ~ N(mean,variance or standard deviation).

How do I know if X ~ N(50,4) the number 4 is variance or standard deviation
because when I put it back into the Z formula it has to be divided by standard deviation?

Thanks.

I thought it was always written as X ~ N( Mean , Standard Deviation )...

The notation people use varies so you'll have to check elsewhere in their work for the system they are using.

In other words, "read your textbook"!

Ok thanks.