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 = 5 and b = 12, what is the length of the hypotenuse of a right triangle?

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If a+b = 10 and ab = 21, what is the value of a^3 + b^3?

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The simple interest on Rs. 4000 at 5% per annum for 2 years is:

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The sides of a triangle are 7, 24, and 25. Is this a right triangle?

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What is the cube of 4?

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A number is increased by 20% and then decreased by 20%. What is the net change?

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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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What is the sum of the first 20 odd numbers?

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If x^2 - 5x + 6 = 0, what are the roots?

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If 2x = 16, what is the value of x?

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