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

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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 LCM of 15 and 20?

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The probability of getting an even number when rolling a die is:

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The sum of the reciprocals of two numbers is 1/4. If one number is 12, what is the other?

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If x + 1/x = 5, what is the value of x^2 + 1/x^2?

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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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A sum of money doubles itself in 5 years at simple interest. What is the rate of interest?

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

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

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