A question regarding road laws (50 zones)

[ILLaViTaR]

I'm resitting my license tomorrow and I'm not 100% sure on speed limits.

The license is in Frankston.

Now it has a lot of industrial roads that are 60 and some residential roads that are 50.

A lot of these 50 roads turn onto 60 zones.

Since I don't know the area well I dunno whether every main road is 50, 60, 70 or 80 etc.

So say I turn out a side road (That is 50) onto a bigger road (still built up though) and it's actually a 70. Since I turned out a side road I won't see a sign instantly so how can I possibly know the limit of the road?

I heard you fail instantly of doing 10km under the limit.

What do I do?