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

A rectangle has an area of 48 cm² and a length of 8 cm. What is its width?

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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 x = 2 and y = 3, what is the value of (x^2 + y^2)?

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If the perimeter of a square is 40 cm, what is the area of the square?

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If a cone has a base radius of 3 cm and height of 4 cm, what is its slant height?

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What is the area of a sector of a circle with radius 14 cm and central angle 90°?

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A car covers a distance of 150 km in 2.5 hours. What is its average speed?

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What is the greatest common divisor (GCD) of 36 and 48?

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The angles of a quadrilateral are in the ratio 3:4:5:6. What is the largest angle?

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A sum of money triples itself in 12 years at simple interest. What is the rate of interest per annum?

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