Negative Decimals

Part of the Decimals, Percents & Ratios section of Coddy's Pre-Algebra journey. Lesson 8 of 56.

The sign rules from Numbers and Operations work for decimals unchanged. Take -3.5 + 1.25. The signs differ, so subtract the sizes: 3.50 - 1.25 is 2.25. The negative number has the larger size, so the answer is negative: -2.25.

On the number line, start at -3.5 and move 1.25 to the right. You do not reach zero, so you land on the negative side, at -2.25. The subtraction of sizes tells you how far from zero you end, and the sign tells you which side.

$Number line from -4 to 1 with -3.5, -2.25 and 0 marked$

From -3.5, a move of 1.25 to the right lands on -2.25.

Taking a bigger decimal from a smaller one crosses zero the same way. In 1.4 - 2.9, the 2.9 taken away is the bigger size, so the result is negative, and 2.9 - 1.4 is 1.5: the answer is -1.5.