In this lesson, we will learn:
- How to estimate the answer to addition statements
- The two methods for estimating sums: front-end estimation and estimation by rounding
- How to check and compare your estimated sums with the exact answer
- An estimation is a rough calculation (or guess) of what the exact answer could be around.
- We use the symbol when estimating; it means “about equal to”
- An estimation is less exact, but it’s easier (faster) to calculate
- When estimating, it is helpful to remember how to round numbers
- You can round to any place value by:
- Keeping all the bigger place values (to its left) and fill in all the smaller place values (to its right) with zeroes.
- Looking at the number in the smaller place value (to its right).
- If that number is 5 or bigger ( 5), round UP.
- If that number is 4 or smaller (< 5), round DOWN. (keep the same value in that digit)
- For a mixed fraction, round to the nearest whole number by looking at the fraction portion. If the fraction is round UP; if the fraction is < round DOWN
- Two methods to estimate sums: frond-end estimation and estimation by rounding
- Front-End Estimation:
1. Add the front digits
2. Write zeroes
- The front digit is the greatest place value out of all your addends (ex. only thousands column; only hundreds column)
- Adding mixed fractions: add the whole number parts only
3. Adjust the estimate
- All the other digits of the answer become zero; skip this step for mixed fractions
- If the back digits can be grouped together to make a group of ten (i.e. one front digit), add to the front digit estimate
- If you are adding mixed fractions, see if the fraction portions can be added to make at least one more whole; if so, add to the estimate
- Estimation by Rounding:
2. Add the rounded numbers
- Round to the greatest place value of the smallest number out of all your addends
- If you are adding mixed fractions, round to the nearest whole number
- You can compare the exact sum and the estimated sum to see how close they are
- An underestimate happens when you round DOWN the addends; the estimated sum is LESS than the exact sum
- An overestimate happens when you round UP the addends; the estimated sum is MORE than the exact sum