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Section 10.2 · Number

Percentages of a quantity

Find a percentage of a quantity, using mental methods built from 10% and 1%.

6 teaching slides 52 practice questions Worked answers for every question

1 · Teaching slidesuse ← → keys

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2 · Key words

ofIn percentage work, “of” means multiply.
mental methodWorking it out in your head by building from 10%.
quantityThe amount you are taking a percentage of.

3 · Summary of the sectionrevise from this

  • 10% is one tenth — divide by 10. This is the building block for everything else.
  • 1% is one hundredth — divide by 100. From 1% you can build any percentage at all.
  • 50% is halving, 25% is dividing by 4, 75% is three quarters.
  • Build the awkward ones: 35% = 10% + 10% + 10% + 5%.
  • 5% is always half of 10%, and 2.5% is half of that.
  • p% of n and n% of p are equal — both are p × n ÷ 100. Use whichever is easier.
  • Over 100% gives more than you started with: 150% of 200 is 300.
  • To go backwards, find 1% first: if 30% is 24, then 1% is 0.8 and 100% is 80.
PDFPrintable worksheet All 52 questions, space to work PDFWorked answers Full solutions, not just the answer

Video lessons1 videos

Math Antics - What Percent Is It?

American mathantics

Finding a percentage of an amount, and expressing one number as a percentage of another.

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4 · Practice52 questions, easiest first

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10.1 Fractions, decimals and percentages
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10.3 Percentage increase and decrease