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

The sides of a triangle are 5 cm, 12 cm, and 13 cm. What type of triangle is it?

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If 2a + b = 10 and a - b = 4, what is the value of a?

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The sum of the squares of two consecutive integers is 145. What are the integers?

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If two complementary angles differ by 30°, what are the angles?

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A sum triples in 20 years at simple interest. What is the rate of interest per annum?

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

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The sides of a triangle are 13 cm, 14 cm, and 15 cm. What is its area?

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A man spends 75% of his income and saves Rs. 600. What is his total income?

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What is the square root of 121?

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