Front end estimating

Front end estimating is rounding the first significant number on any calculation as a rough estimate.

By rounding the first number in a sum you can make it easier but the answer wont be exactly correct

Sometimes the front end is more important.

Example 1

Estimate the following sum:

$4026+398+42$

Adding $4026+398+42$ is tricky.

But adding $4000+400+40$ is easy.

NOTE:

The real answer is $4466$ and so you can see that $4440$ is a worthy estimate.