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Decimals and Percentages

9 min read

Decimals

A decimal uses a decimal point to show parts smaller than one. The places to the right of the point are tenths, hundredths, thousandths and so on. In 3.46 the 4 is 4 tenths and the 6 is 6 hundredths.

Place valueA place value chart for the number 345.67: 3 hundreds, 4 tens, 5 ones, then after the decimal point 6 tenths and 7 hundredths.Hundreds3Tens4Ones5.Tenths6Hundredths7345.67 = 300 + 40 + 5 + 0.6 + 0.07
Place values around the decimal point
ThousandsHundredsTensOnes.TenthsHundredths
3.46
Worked exampleAdding decimals

Work out .

  1. Write 0.8 as 0.80 so both have two decimal places.
  2. Line up the points and add.

Answer: 3.55

Percentages

Percentage
A number out of 100. The symbol % means "per hundred". 45% means 45 out of 100.
A percentage on a 100-square gridA grid of 100 small squares with 35 shaded. This shows 35 out of 100, which is 35 percent, the fraction 35 over 100 or 7 over 20, and the decimal 0.35.35 out of 100= 35%= 35/100 = 7/20= 0.35
How to find a percentage.
Try itPart of a whole

Choose how many parts are shaded. See the fraction, decimal and percentage.

Worked examplePercentage of an amount

Find 15% of 2 000 shillings.

  1. Write 15% as a fraction of 100.
  2. Multiply by the amount.

Answer: 15% of 2 000 shillings is 300 shillings.

Check yourself Write 0.6 as a percentage.
Check yourself A learner scores 18 out of 24. What percentage is that?

Key terms

Decimal point
The dot that separates whole numbers from parts.
Percentage
A number out of 100, written with %.

Summary

  • Decimal places to the right of the point are tenths, hundredths, thousandths.
  • Line up decimal points when adding or subtracting.
  • Percentage = part ÷ whole × 100.
  • Fractions, decimals and percentages are three ways to write the same amount.
Fractions Units