Revision Notes for Class 8 Maths Chapter 8: Fractions in Disguise (Percentages)

Condensed revision notes for Class 8 Maths Chapter 8: Fractions in Disguise (Percentages) – Ganita Prakash. These Class 8 Mathematics Chapter 8 notes are ideal for quick revision just before exams.

Last Updated: September 23, 2026

• Percentage: a fraction/ratio expressed with denominator 100; x% = x/100.
• Fraction → percentage: multiply the fraction by 100 and add the % sign.
• Percentage of a quantity: x% of N = (x/100) × N.
• Commutative identity: x% of y = y% of x (both equal xy/100).
• Profit % = (Profit ÷ CP) × 100; Loss % = (Loss ÷ CP) × 100 — always calculated on Cost Price, not Selling Price.
• Marked Price & Discount: SP = MP × (1 − discount%/100).
• Successive percentage changes multiply as factors — e.g. (1±a/100)(1±b/100)… — they do NOT simply add.
• Increase then equal decrease (or vice versa) always gives a net decrease of a²/100 percent.
• Simple Interest: SI = P × r × t ÷ 100; Amount = P + SI.
• Compound Interest: Amount = P(1 + r/100)^t; CI = Amount − P.
• Compound growth/decline over multiple periods with different rates: multiply the successive factors together.
• GST/tax addition: Final price = Price × (1 + GST%/100).
• Reverse percentage: Original value = Final value ÷ (1 ± r/100) — divide, don’t subtract the percentage.
• “Buy m get n free” effective price fraction: m ÷ (m+n) of the original price.
• Rule of thumb: always work with multiplicative factors (not additive percentages) whenever a quantity changes more than once.

More on this chapter: Solutions | Extra Questions | Class 8 Maths Book | Formulas Handbook

Frequently Asked Questions

How is a fraction converted into a percentage?
A fraction is converted into a percentage by multiplying it by 100 and adding the percent sign, so three-fourths becomes seventy-five percent because three-fourths multiplied by 100 equals 75.

Why are percentages useful for comparing quantities?
Percentages express quantities out of a common base of 100, which makes it easy to compare different proportions or changes directly, even when the original quantities being compared are of very different sizes.

Written by Satish

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