Addition, subtraction, and estimation: FAQ

Rounding numbers is helpful when we want to estimate sums or differences. For example, if we want to add $235$‍ and $286$‍, we might round both numbers to the nearest hundred and estimate that the sum is around $500$‍.

There are many ways we can add numbers together. One way is to break one of the numbers down and add or subtract each part separately. Another strategy is to use groups of $10$‍ or $100$‍ or by using a number line.

When we regroup, we carry over numbers from one place value to another. For example, when we add $38$‍ and $47$‍, we end up with $15$‍ in the ones place. But we can't write $715$‍ as the sum because we only use one digit in the ones place. So we regroup by carrying over the $10$‍ from the $15$‍ into the tens place, which gives us a sum of $85$‍.

We use addition, subtraction, and estimation in our everyday lives all the time! For example, when we go to the store, we might estimate how much our items will cost before we get to the checkout line. Or when we're baking, we might need to add or subtract measurements to get the right amount of ingredients.