How do you estimate 555?

Answer 1

The front end estimate is 600. But estimating a single number, in isolation and without context, is a complete waste of time.

If I had to add 555 to 1 trillion, I would estimate it as 0. If I had to add 555 to 0.0000000001, I would use the number as given - not use an estimate.

Answer 2

To the nearest ten, 560