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 cylinder has a radius of 7 cm and height of 10 cm, what is its volume?

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A train 150 m long passes a pole in 15 seconds. What is its speed?

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

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

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If sin(A) = 1/2 and A is acute, what is the value of A?

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If a:b = 7:9 and b:c = 5:6, what is a:c?

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The perimeter of a rectangle is 50 cm, and its length is 15 cm. What is its width?

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If the radius of a circle is 7 cm, what is its circumference?

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If x^2 + 4x + 4 = 0, what is the value of x?

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

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