Math 7 · Unit 3, Lesson 5: Dividing Signed Numbers · Tile 3 of 4
Fractions and Decimals
Flip and multiply
Flip and multiply
Dividing by a fraction is the same as multiplying by its reciprocal, the fraction flipped upside down. Dividing by 12 asks how many halves fit, and two halves fit in every 1, so it's the same as multiplying by 2. Figure out the sign first, the same way as always. Then flip and multiply.
The word
| Elle (math-speak) | Finn (plain English) |
|---|---|
| Reciprocal | A fraction flipped upside down. The reciprocal of 23 is 32. A number times its reciprocal is 1. |
Sign first, then flip
To divide by a fraction, multiply by its reciprocal. The sign rules for division apply to all rational numbers.
Sign first. Then flip the second fraction and multiply. Fractions and decimals follow the same sign rules as whole numbers.
Flip only the number you divide by, never the first one. And it's the fraction that flips, not the sign.
The first and third examples are from the North Carolina unpacking document for this standard.
NC standard: NC.7.NS.2.