Skill: Estimate differences by rounding

To estimate a difference, round both numbers independently to the nearest ten or hundred. Then subtract the rounded numbers.

Example: Estimate $674-238$ by rounding to the nearest ten.

1. Round each number:

   • $674$ rounds to $670$ because $4$ is less than $5$.
   • $238$ rounds to $240$ because $8$ is $5$ or more.

2. Subtract the rounded numbers:

$$670-240=430$$

So, the estimated difference is:

$$\boxed{430}$$

The exact difference is $436$, so $430$ is a reasonable estimate. The estimate is a little less because $674$ was rounded down and $238$ was rounded up.