Topic Details (Notes format)

How to Solve Proportions (Cross-Multiplication)

Subject: Mathematics

Book: Maths Mastery

Proportions equate two ratios, like a/b = c/d. Cross-multiplication states ad = bc. For example, if 2/5 = x/15, then 2 × 15 = 5 × x, meaning 30 = 5x, so x = 6. Proportions answer real-world questions: “If 2 liters costs ₹100, what does 5 liters cost?” or “If 3 out of 10 students prefer a subject, how many out of 50 might prefer it?” The technique is vital for scaling recipes, resizing images, or solving geometry similarity. Consistent practice ensures you can set up and solve ratio-based statements in a single, efficient step.

Practice Questions

If a square has a perimeter of 64 cm, what is its area?

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What is the sum of the first 10 positive even numbers?

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What is the HCF of 72 and 120?

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If x:y = 4:5 and y:z = 2:3, what is x:z?

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If the sides of a triangle are 6 cm, 8 cm, and 10 cm, what is the area of the triangle?

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If the average of five consecutive odd numbers is 25, what is the largest number?

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A sum of money doubles itself in 5 years at simple interest. What is the rate of interest?

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If the product of two numbers is 120 and their sum is 26, what are the numbers?

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If x - y = 5 and x + y = 15, what is the value of x?

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A train 120 meters long is moving at a speed of 54 km/h. How long will it take to pass a pole?

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