How do you estimate 634?

Answer 1

The front end estimate is 600. But estimating a single number, in isolation and without context, is a complete waste of time. It all comes down to the context of what needs to be done with the number.

If I had to add 634 to 1 trillion, I would estimate it as 0.
If I had to add 634 to 0.0000000001, I would use the number as given, or possibly the front end estimate. If I had to divide it by 6, I would estimate it as 630, because 630/6 = 105. If I had to divide it by 50, I would estimate it as 650, because 650/50 = 13.

Answer 2

To the nearest ten, 630