Scale quantities down using a ratio

Scaling a quantity down means multiplying it by a ratio less than 1, such as $3/4$ , so that the new quantity maintains a multiplicative relationship with the original; equivalent ratios, ratio tables, and double number lines can show this relationship. The learner distinguishes proportional reduction from subtracting a fixed amount and determines missing quantities in familiar measurement and real-world contexts using whole-number and fraction ratios, without extending to more advanced algebraic or generalized scale-factor cases.

Detailed Explanation: Scale quantities down using a ratio

To scale a quantity down, multiply it by a ratio less than $1$ . The ratio tells how much of the original amount to keep.

Example

A recipe uses $8$ cups of flour. You want to make only $\frac{3}{4}$ of the recipe. How much flour do you need?

Identify the original quantity: $8$ cups.
Identify the scale-down ratio: $\frac{3}{4}$ .
Multiply:

8 \times \frac{3}{4}

Divide $8$ by $4$ , then multiply by $3$ :

8 \times \frac{3}{4} = \left(8 \div 4\right)\times 3 = 2\times 3 = 6

You need $6$ cups of flour.

The ratio $\frac{3}{4}$ means the new amount is three out of every four equal parts of the original amount. This is different from subtracting a fixed amount, such as taking away $2$ cups. Scaling keeps the same multiplicative relationship for every quantity in the recipe.

Learn by doing: Scale quantities down using a ratio

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Ratios - Equivalent, Shrinking Recipes with Integer Multiples - Fractions

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