Explain to students that with estimated sums you first round the numbers and then solve the problem. The problem of 3,998 + 1,984 for example can be solved by using the estimated problem of 4,000 + 2,000. With another example show students that you can round the numbers to a hundreds or thousands number. Discuss the statements about rounding to hundreds or thousands numbers. Remind students that the way you round makes a difference to your estimate. If you want to stay closer to the exact sum, you can round to a closer number (say a hundreds number), rather than rounding to the nearest thousand. Practice estimated sums by asking students to match the best estimated problem for the three given problems. Then practice estimating the sum and determining if the total is more or less than the exact sum. Ask students to explain their strategy. Finally practice estimation in context that students might recognize.
To check that students are able to estimate the sum to 10,000 ask them the following questions:
- Why is it useful to be able to estimate the sum?
- If you round the numbers as large as possible, are you closer to the exact sum or further away from it?