What is the estimated answer to 43?

Answer 1

The front end estimate is 40. 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 43 to 1 trillion, I would estimate it as 0.
If I had to add 43 to 0.0000000001, I would use the number as given. If I had to divide it by 4, I would estimate it as 44 because 44/4 = 11. If I had to divide it by 3, I would estimate it as 42 because 42/3 = 14.

Answer 2

To the nearest ten, 40.