how can estimating help you add two- digit numbers?
If you round the numbers and then add them, you'll be estimating.
Example: 27 + 51 is about 30 + 50. Since 3 + 5 = 8, then 30 + 50 is about 80.
Example: 27 + 51 is about 30 + 50. Since 3 + 5 = 8, then 30 + 50 is about 80.