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

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A rectangle has a length of 10 cm and a width of 5 cm. What is the diagonal of the rectangle?

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If the sides of a triangle are 6 cm, 8 cm, and 10 cm, what is the area of the triangle?

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If sin(x) = 3/5 and x is in the first quadrant, what is cos(x)?

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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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If 5x - 2 = 13, what is the value of x?

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

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What is the cube of 4?

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If x + y = 10 and xy = 21, what is the value of x³ + y³?

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