What biggest number can be rounded off to 100?

Answer 1

There isn't any "biggest".

If I say it's 149, then you'll say I'm wrong, because 149.5 is bigger and still rounds to 100.

If I say it's 149.99, then you'll say I'm still wrong, because 149.999 is bigger and still rounds to 100.

Whatever number anybody says, there's always a bigger one that still rounds to 100.