Grade: 3, Topic(s): addition/subtraction

## Purpose

To add 25 to any number using mental computation.

None

Have children add 25 to each number you say. You can suggest adding 20 and then adding 5 more or ask children to offer their own strategies. Start with numbers less than 100. When children are ready, progress to three-digit numbers. You may want to record the numbers in a table with the headings *N *and *N *+ 25.

Part 1 starts at 0, allowing focus to be given to the +25 strategy of adding 10, adding 10, and adding 5 more. Part 2 adds 25 in a “chain” starting at 27. The extension starts at a larger number.

Let’s start at 0 and add 25. Then we’ll add 25 again to *that *result—and keep going until we get to at least 300.

- 0, 25, 50, 100…250, 275, 300

*If children need more practice or are enjoying their mastery, repeat. If children are ready to move on, go to Part 2.*

Let’s start at 27 and add 25. Then we’ll add 25 again to *that *result – and keep going until we get to at least 300.

Number sequence:

- 27, 52, 77, 102, 127, 152,177, 202, 227, 252, 277, 302

*If children need more practice, repeat. Or, when children seem excited for a new challenge, move to the extension.*

Let’s start at 68 and add 25. Then we’ll add 25 again to *that *result and keep going until we reach at least 300.

- 68, 93, 118, 143, 168, 193, 218, 243, 268, 293, 318

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