Recipe Scaling Adventures — Ratios & Proportions worksheet for Grade 7.
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A ratio compares two quantities (like 2 cups flour to 1 cup sugar, written as 2:1). A proportion is an equation showing that two ratios are equal (like 2/1 = 4/2, meaning both maintain the same relationship). In recipe scaling, you write a proportion to find the new ingredient amount while keeping the same ratio of ingredients.
Cross-multiplication is a shortcut that works because of the property of equal ratios. If a/b = c/d, then a×d = b×c. For example, if 2 cups flour serves 4 people and you need flour for 8 people, you set up 2/4 = x/8. Cross-multiplying gives 2×8 = 4×x, so 16 = 4x, and x = 4 cups. It's faster than finding a common denominator.
Have them verify three things: (1) Did they multiply or divide the original amount by the scale factor in the correct direction? (2) Are they working with the same units (e.g., cups to cups, not cups to tablespoons)? (3) Did they apply the scale factor consistently to ALL ingredients? A common mistake is calculating the scale factor correctly but then using it inconsistently across ingredients.
Use concrete examples. If doubling a recipe (scale factor of 2) means multiplying by 2, then scaling to half a recipe (scale factor of 0.5) means multiplying by 0.5, which is the same as dividing by 2. Practice both directions with the same recipe so they see that the proportion setup stays identical—only the numbers change. This builds confidence that the method is reliable regardless of direction.
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Fractions scale just like whole numbers and decimals. Multiply the fraction by the scale factor: 3/4 × 2 = 6/4 = 1 1/2 cups (for doubling). If students struggle with fraction multiplication, have them convert to decimals first (3/4 = 0.75, so 0.75 × 2 = 1.5 = 1 1/2). Both methods work; let them choose what's comfortable. The key is applying the scale factor consistently.