Adding 25 – Elementary Math

Purpose

To add 25 to any number using mental computation.

Materials

None

Overview

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.

About the sequence

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.

Part 1

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.

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.

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