Ratios & scaling
A ratio is parts, not amounts. Add the parts, find one part, then multiply. To scale, use one scale factor (servings you want ÷ servings in the recipe) for every ingredient, then taste.
Units first. 1 tsp = 5 mL, 1 tbsp = 15 mL, 1 cup = 250 mL in Canadian recipes (p.11). °C = (°F − 32) × 5 ÷ 9. Round to what a kitchen can measure. Pencil and paper only: if you cook any of it, have an adult nearby if you’re under 18.
One step
Ratios, scale factors, units and unit price.Jar dressing
You want 160 mL of 3 : 1 vinaigrette (p.8). How much oil and how much vinegar?
Feed ten
A pasta recipe serves 4 and uses 300 g of pasta. What is the scale factor for 10 people, and how much pasta do you need?
Spoons and cups
Convert to millilitres: 3 tablespoons, and 2 cups (Canadian recipe).
Unit price
A 1.5 kg bag of rice costs $6.00. What is the price per 100 g, like a shelf tag shows (p.12)?
Two or three steps
Show each step, then check it makes kitchen sense.Bread by percentages
A lean bread is 100 : 65 : 2 : 1 for flour, water, salt and yeast (p.9). With 600 g of flour, how much water, salt and yeast? How heavy is the whole dough?
Scaling down
A muffin recipe makes 12 with 375 mL flour, 150 mL milk and 3 eggs. You want 9. Find the scale factor and each amount. What do you do about the eggs?
Oven dial
An old recipe says 325 °F. Convert it to °C to one decimal place. What would you set a Celsius oven to?
A bowl of chili
A pot of bean chili for 8 uses 2 cans of beans at $1.29 each, tomatoes $1.80, an onion $0.60, peppers $2.00 and spices $0.70, served over 500 g of rice at $0.40 per 100 g. Cost per bowl?
Better buy?
Yogurt: 750 g for $4.49, or 2 kg for $9.99. Find each price per 100 g. When is the bigger tub not the better deal?
Plan from the finish
A chicken roasts for 1½ hours and rests 15 minutes. Prep takes 20 minutes. Dinner is at 6:30 PM. When must it go in the oven, and when do you start?
Equations and circles
From A1–A2 (pp.17–18). Use a calculator for π and roots.Per-person rule
Oatmeal uses 40 g per person, so g = 40p. How many people does a 1 kg bag feed? Solve 1,000 = 40p.
Solve for °C
Use °F = 1.8 × °C + 32 (p.17). A pizza recipe says 425 °F. Solve 425 = 1.8C + 32 to one decimal place.
Round to square
A round pan is 25 cm across. Find its area (A = πr²). What square pan has about the same area? Solve s² = A.
How deep?
You have 1.2 L (1,200 cm³) of batter. How deep is it in a 20 × 20 cm pan? In a 23 × 33 cm pan? Which bakes faster?
Your turn to be the recipe tester
- Pick a real recipe at home and choose a new number of servings.
- Write one scaling, one unit and one cost question about it.
- Solve them on a separate line, then swap with someone and check each other.
My problem, and my worked answer:
Try every problem first, then check here. Wrong answers are useful: find the step where your work and the key split apart.
The key never prints with Print my work or Print blank. Open it to get its own Print the answer key button.
Answer key
Worked solutions. Your steps can look different and still be right. Kitchen answers are rounded to what you can measure.