In this lesson, students will attempt to find a three-digit address number that meets certain criteria.

You may wish to draw a house, similar to the one shown below, on the board or overhead projector. Be sure that the house has three slots where the digits of the address number could be placed.

Hold up the Numeral Cards for 6, 0, and 2.

Numeral Cards

Ask students what they notice about the three-digit number formed by those digits. They may notice that:

- the digits are different
- the sum of the digits is 8
- the digits form the number 602.

Ask students if there is another way to get a sum of 8 using any of the numeral cards. However, the digits must be different and the number formed by the three digits must be greater than 600. Students may need time to think about the various possibilities. A class discussion should yield only one other possible solution: **701**.

Students will solve a similar problem in today’s lesson. However, there will be multiple solutions possible. Present the following problem to students:

- The house number has three different digits.
- The sum of the three digits is 12.
- The number is greater than 480.
- What could the address number be? List all possible numbers.

Distribute one copy of the Create an Address Number Activity Sheet to each student.

Create an Address Number Activity Sheet

Have students cut the number tiles from the bottom of the activity sheet to use as digits.

Allow students some time to work on the problem individually. Then, allow students to work with a partner to discuss their answers. In particular, they should attempt to create a complete list, which may be accomplished by combining the answers they attained individually. Students should compare their lists, noting any "repeats" or missing number combinations.

Lead a discussion to arrive at a conclusion. The discussion should include the need for keeping an organized list, so that students can be sure when they have found all possibilities. Students should also discuss how house numbers were found. For example, they might mention that they tried to find a set of three numbers that met one criteria (for instance, the set had a sum of twelve) but then removed those sets that did not meet the other criteria (for example, remove sets with digits repeated). Continue the discussion until students are convinced that they have found all possible address numbers.

After the discussion, you may wish to ask students the questions listed in the *Extensions *section.

**Reference**

Cook, Marcy. "IDEAS: Possible Solution Sets" The Arithmetic Teacher Vol.36, No.5 (January, 1989) pp. 19 -24.