Adding and Subtracting Fractions and Decimals

Adding Decimals

To add decimals, use a different color for each addend.

For example, to model 0.22 + 0.59:

• Fill 22 sections in a hundredths grid in one color
• In the same grid, fill 59 other sections with a different color.

To find sums greater than 1, use more than one hundredths grid. For example, to model 1.21 + 0.77 + 0.16:

• Fill 121 sections (one complete grid and 21 sections on a second grid) in the first color.
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• Fill 77 sections in a second color.
• Fill 16 sections in a third color. (Fill two grids completely. Fill the remaining 14 sections on the third grid.)

Adding Fractions

To add like fractions, use a different color for each addend. The grid size depends on the denominator of the fractions. (To add unlike fractions, first rewrite them using the same denominator.)

For example, to model

:

• Click the arrow above a grid, and choose "eighteenths grid."
• Fill 7 sections of the grid in one color.
• Fill 5 sections of the grid in a second color.

The 12 filled sections represent the sum

.

Subtracting Fractions and Decimals

To subtract on a grid, cross out squares.

For example, to model

:

• Click the arrow above a grid, and choose "twelfths grid."
• Fill 11 sections of the grid.
• Click the square with an "x" at the top left of the tool.
• Click 5 filled sections to cross them out. (To cross out several sections at once click and drag.)