Dividing is Multiplying
Dividing by a number is identical to multiplying by its reciprocal: a ÷ b = a × (1/b). In Grade 6 Saxon Math Course 1 (Chapter 7: Fractions and Geometric Concepts), students use the Keep-Change-Flip method to convert any fraction division into multiplication. Keep the first number unchanged, change the division sign to multiplication, then flip the second number to its reciprocal. For example, 4 ÷ 2/3 becomes 4 × 3/2 = 12/2 = 6. This technique applies to whole numbers, fractions, and mixed numbers (after converting mixed numbers to improper fractions first).
Key Concepts
Property Dividing by a number is the same as multiplying by its reciprocal. For any numbers $a$ and $b$ (where $b \ne 0$), $a \div b = a \times \frac{1}{b}$.
Examples Shawna dividing $2\frac{2}{3}$ cups for 4 plants ($2\frac{2}{3} \div 4$) is the same as finding $\frac{1}{4}$ of the food ($2\frac{2}{3} \times \frac{1}{4}$). To solve $1\frac{3}{5} \div 4$, you can instead calculate $1\frac{3}{5} \times \frac{1}{4} = \frac{8}{5} \times \frac{1}{4} = \frac{2}{5}$. Compare: $4\frac{1}{2} \div 3$ is equal to $\frac{1}{3} \times 4\frac{1}{2}$, since dividing by 3 is the same as multiplying by $\frac{1}{3}$.
Explanation Why is dividing by 4 the same as multiplying by $\frac{1}{4}$? It’s two ways of asking the same thing! Dividing asks 'how many groups of 4 can I make?' while multiplying by $\frac{1}{4}$ asks 'what is one fourth of my stuff?' Both questions split your total into four equal shares, leading to the exact same answer.
Common Questions
What is the Keep-Change-Flip method for dividing fractions?
Keep the first number as-is, change the division sign to multiplication, and flip the second number (take its reciprocal). Then multiply normally.
What is the reciprocal of 2/3?
The reciprocal of 2/3 is 3/2. Flipping a fraction swaps its numerator and denominator.
Why does dividing by a number equal multiplying by its reciprocal?
Because multiplying both sides of a÷b by b gives a. Multiplying by 1/b achieves the same result since b × 1/b = 1.
How do you divide 5/6 by 2/3 using Keep-Change-Flip?
Keep 5/6, change ÷ to ×, flip 2/3 to 3/2. Then 5/6 × 3/2 = 15/12 = 5/4 = 1 1/4.
What is the reciprocal of a whole number like 4?
Write 4 as the fraction 4/1, then flip it to get 1/4. So 4 ÷ 4 = 4 × 1/4 = 1.