# IGCSE Mathematics Foundation: Ratio and Proportion

## Scheme of work: IGCSE Foundation: Year 10: Term 3: Ratio and Proportion

#### Prerequisite Knowledge

1. Understanding Equivalent Fractions
• Concept: Recognizing and generating equivalent fractions by multiplying or dividing the numerator and denominator by the same number.
• Example: $\frac{1}{2} = \frac{2}{4} = \frac{3}{6}$
2. Converting Between Fractions, Decimals, and Percentages
• Concept: Understanding how to convert fractions to decimals and percentages, and vice versa.
• Example: $\frac{1}{4} = 0.25 = 25\%$ $0.75 = \frac{3}{4} = 75\%$

#### Success Criteria

1. Use Ratio Notation, Including Reduction to Its Simplest Form and Its Various Links to Fraction Notation
• Objective: Understand and use ratio notation, and simplify ratios by finding the greatest common divisor (GCD). Recognize the relationship between ratios and fractions.
• Example: $\text{Simplify the ratio } 8:12 \text{ to } 2:3.$ $\text{Recognize that } 2:3 \text{ can also be written as the fraction } \frac{2}{3}.$
2. Use and Interpret Maps and Scale Drawings
• Objective: Understand how to use scale drawings and maps to determine actual distances.
• Example: $\text{If a map has a scale of } 1:100000, \text{ then 1 cm on the map represents 1 km in reality.}$
3. Divide a Quantity in a Given Ratio or Ratios
• Objective: Divide a quantity into parts according to a given ratio.
• Example: $\text{Divide } 60 \text{ into the ratio } 2:3.$ $\text{Total parts } = 2 + 3 = 5.$ $\text{Each part } = \frac{60}{5} = 12.$ $\text{So, the two parts are } 2 \times 12 = 24 \text{ and } 3 \times 12 = 36.$
4. Use the Process of Proportionality to Evaluate Unknown Quantities
• Objective: Use the concept of proportionality to find unknown quantities when two values are in proportion.
• Example: $\text{If } 4 \text{ pencils cost } \2, \text{ how much do 10 pencils cost?}$ $\text{Proportion: } \frac{4}{2} \rightarrow \frac{10}{x}$ $4x = 20 \rightarrow x = 5.$ $\text{So, 10 pencils cost } \5.$
5. Calculate an Unknown Quantity from Quantities that Vary in Direct Proportion
• Objective: Determine unknown values in problems involving direct proportion.
• Example: $\text{If } y \text{ is directly proportional to } x \text{ and } y = 8 \text{ when } x = 2, \text{ find } y \text{ when } x = 5.$ $y = kx \rightarrow 8 = 2k \rightarrow k = 4.$ $y = 4x \rightarrow y = 4 \times 5 = 20.$
6. Solve Word Problems about Ratio and Proportion
• Objective: Apply the concepts of ratio and proportion to solve real-life word problems.
• Example: $\text{A recipe requires } 3 \text{ cups of flour for every } 2 \text{ cups of sugar. If you have } 6 \text{ cups of flour, how much sugar do you need?}$ $\text{Ratio of flour to sugar is } 3:2.$ $\frac{3}{2} \rightarrow \frac{6}{x} \rightarrow 3x = 12 \rightarrow x = 4.$ $\text{So, you need } 4 \text{ cups of sugar.}$

#### Key Concepts

1. Use Ratio Notation, Including Reduction to Its Simplest Form and Its Various Links to Fraction Notation
• Concept: A ratio compares two quantities and can be simplified by dividing both terms by their greatest common divisor (GCD). Ratios can also be represented as fractions.
• Example: $\text{The ratio } 8:12 \text{ simplifies to } 2:3 \text{ by dividing both terms by 4.}$ $\text{The ratio } 2:3 \text{ can be written as the fraction } \frac{2}{3}.$
2. Use and Interpret Maps and Scale Drawings
• Concept: Scale drawings and maps use a scale to represent real distances. Understanding the scale allows you to convert measurements on the drawing or map to actual distances.
• Example: $\text{A map scale of } 1:100000 \text{ means 1 cm on the map represents 1 km in reality.}$
3. Divide a Quantity in a Given Ratio or Ratios
• Concept: To divide a quantity into a given ratio, you first find the total number of parts, then divide the quantity by this total to find the value of each part, and finally multiply by the number of parts in each ratio segment.
• Example: $\text{To divide 60 into the ratio } 2:3, \text{ first find the total parts } (2 + 3 = 5).$ $\text{Each part } = \frac{60}{5} = 12.$ $\text{So, the two parts are } 2 \times 12 = 24 \text{ and } 3 \times 12 = 36.$
4. Use the Process of Proportionality to Evaluate Unknown Quantities
• Concept: When two quantities are proportional, their ratio remains constant. This concept can be used to find unknown quantities by setting up a proportion and solving for the unknown.
• Example: $\text{If 4 pencils cost } \2, \text{ the cost of 10 pencils can be found using the proportion } \frac{4}{2} \rightarrow \frac{10}{x}.$ $4x = 20 \rightarrow x = 5.$ $\text{So, 10 pencils cost } \5.$
5. Calculate an Unknown Quantity from Quantities that Vary in Direct Proportion
• Concept: In direct proportion, the ratio between two quantities remains constant. If $$y$$ is directly proportional to $$x$$, then $$y = kx$$, where $$k$$ is the constant of proportionality.
• Example: $\text{If } y \text{ is directly proportional to } x \text{ and } y = 8 \text{ when } x = 2, \text{ then } y = kx \rightarrow 8 = 2k \rightarrow k = 4.$ $\text{To find } y \text{ when } x = 5, \text{ use } y = 4x \rightarrow y = 4 \times 5 = 20.$
6. Solve Word Problems about Ratio and Proportion
• Concept: Applying the concepts of ratio and proportion to real-life situations involves setting up and solving equations based on the given ratios or proportions.
• Example: $\text{If a recipe requires } 3 \text{ cups of flour for every } 2 \text{ cups of sugar, and you have } 6 \text{ cups of flour, how much sugar do you need?}$ $\text{Set up the proportion } \frac{3}{2} \rightarrow \frac{6}{x} \rightarrow 3x = 12 \rightarrow x = 4.$ $\text{So, you need } 4 \text{ cups of sugar.}$

#### Common Misconceptions

1. Use Ratio Notation, Including Reduction to Its Simplest Form and Its Various Links to Fraction Notation
• Common Mistake: Not simplifying ratios correctly or misunderstanding the relationship between ratios and fractions.
• Example: $\text{Incorrect: Simplifying the ratio } 8:12 \text{ to } 4:6 \text{ instead of } 2:3.$ $\text{Incorrect: Writing the ratio } 2:3 \text{ as the fraction } \frac{3}{2}.$
2. Use and Interpret Maps and Scale Drawings
• Common Mistake: Misinterpreting the scale on maps or drawings, leading to incorrect calculations of actual distances.
• Example: $\text{Incorrect: If the scale is } 1:100000, \text{ then 1 cm on the map represents 1000 km instead of 1 km.}$
3. Divide a Quantity in a Given Ratio or Ratios
• Common Mistake: Incorrectly dividing the quantity by the total number of parts or not properly multiplying by the ratio parts.
• Example: $\text{Incorrect: To divide 60 into the ratio } 2:3, \text{ calculating each part as } 60 \div 2 \text{ and } 60 \div 3.$ $\text{Correct: Each part } = \frac{60}{5} = 12 \text{, then } 2 \times 12 = 24 \text{ and } 3 \times 12 = 36.$
4. Use the Process of Proportionality to Evaluate Unknown Quantities
• Common Mistake: Setting up the proportion incorrectly or solving the proportion inaccurately.
• Example: $\text{Incorrect: If 4 pencils cost } \2, \text{ setting up the proportion as } \frac{4}{x} = \frac{2}{10}.$ $\text{Correct: The proportion is } \frac{4}{2} \rightarrow \frac{10}{x} \rightarrow 4x = 20 \rightarrow x = 5.$
5. Calculate an Unknown Quantity from Quantities that Vary in Direct Proportion
• Common Mistake: Misunderstanding the constant of proportionality or not using it correctly to find the unknown quantity.
• Example: $\text{Incorrect: If } y \text{ is directly proportional to } x \text{ and } y = 8 \text{ when } x = 2, \text{ then } y = 4x \text{ is incorrectly applied as } y = 4 + x.$ $\text{Correct: Use the correct proportional relationship } y = 4x \rightarrow y = 4 \times 5 = 20.$
6. Solve Word Problems about Ratio and Proportion
• Common Mistake: Misinterpreting the problem or setting up incorrect ratios or proportions.
• Example: $\text{Incorrect: If a recipe requires } 3 \text{ cups of flour for every } 2 \text{ cups of sugar, and you have } 6 \text{ cups of flour, calculating the sugar needed as } 6 \times 3 = 18 \text{ cups of sugar}.$ $\text{Correct: Set up the proportion } \frac{3}{2} \rightarrow \frac{6}{x} \rightarrow 3x = 12 \rightarrow x = 4.$ $\text{So, you need } 4 \text{ cups of sugar.}$

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