Decimal subtraction is one of a series of Labs to help you understand and learn to use decimals. I think you will find it fun because it uses random numbers and it will help you visualize decimal operations. Take a look at Decimal Addition and Decimal Multiplication and Decimal Division. Remember like all of our spreadsheets you can look at and change the rules to try different things.

# Category: Addition/Subtraction

# Adding Machine

Multiplication is often thought of as repeated addition. By building a times table by using a repeated addition rule you will have a fun practice of the multiplication facts, and you will learn to build rules in spreadsheets. Rules let you program spreadsheets to do remarkable things like make the multiplication table in just a couple of easy steps.

# More Number Lines

We use rules to build new numberlines. For example we can start in the middle and go both forward or backward using adding and subtracting rules. You can even generate and experiment with negative numbers by subtracting below 0. As you build numberlines on spreadsheets you are building them in your mind. And by thinking of numberlines in terms of rules you are getting ready for algebra.

# Build a House

Spreadsheets with their natural grid make a great, though not entirely flexible, platform for architectural design and for working with shapes. Build a house introduces students to using spreadsheets to create floor plans and to measure area. Most spreadsheets have amazing graphic flexibility. You may want to encourage students to use spreadsheets for art. Here is an incredible example: http://www.spoon-tamago.com/2013/05/28/tatsuo-horiuchi-excel-spreadsheet-artist/

# Addition Table

From here on students can go in most any order they choose. They can start with addition or with multiplication. They should imagine themselves on an elevator able to go up or down anytime they want, to find interesting floors to explore. **NOTE**: The addition table, like the other tables, goes up and to the right to link their patterns with graphing and further work with functions. They thus have a horizontal and a vertical axis that they use to build their rules. The best rules needed to build this table requires the use of “absolute” addressing. Normal or “relative” addresses are patterns that copy from one area of a spreadsheet to another. Absolute or fixed addresses refer to a specific or fixed cells. You can fix an address by column in a rule by putting a $ sign in front of the letter or in a row by putting a $ sign in front of its number. For example: **= $J15 or =J$15, or =$J$15.**