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

What is the HCF of 48 and 180?

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A man invests Rs. 5000 at 5% per annum simple interest. What is the total amount after 3 years?

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If a:b = 5:7 and b:c = 6:11, what is a:c?

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What is the remainder when 5^100 is divided by 3?

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If sin(A) = 3/5 and cos(B) = 5/13, where A and B are acute angles, what is sin(A+B)?

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If 8x = 512, what is the value of x?

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If the angles of a triangle are in the ratio 2:3:4, what is the measure of the largest angle?

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What is the value of x if 3x + 7 = 16?

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If the ratio of two numbers is 3:5 and their HCF is 4, what are the numbers?

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If a = 2 and b = 3, what is the value of (a^2 + b^2)?

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