DeepMaths / Fun Maths

Fun Maths Book 2 Online Learning Programme

For Year 4 and Year 5

Chapter 5: Decimals and Percentages

Decimals and Percentages

Keep decimal points aligned, move digits by place value, and understand percent as out of 100.

Fun Maths Book 2 pages 69-774 minutes

AI teacher

Press Start to hear a short classroom-style explanation. If sound is unavailable, the full script is shown below.

Voice: Browser voice

Workbook pages

Fun Maths Book 2 pages 69-77

Add and subtract decimals, multiply or divide by 10, 100 and 1000, and connect percentages to parts out of 100.

AI explanation

The AI teacher uses a decimal place-value chart to show that digits move into new columns when multiplying or dividing by powers of 10. Percentages are shown as shaded hundred grids.

  1. 1The decimal point stays fixed in written decimal addition and subtraction.
  2. 2Digits move left when multiplying by 10, 100 or 1000.
  3. 3Digits move right when dividing by 10, 100 or 1000.
  4. 4A percentage tells how many parts out of 100.

Think with the AI teacher

Today we will connect decimals and percentages to place value. The digits move into new homes; the decimal point is our marker.

Question 1

Pause 4s

When adding 4.8 and 3.65, why should 4.8 become 4.80?

After thinking

The zero holds the hundredths place so the columns line up.

Good noticing. Placeholders help us compare equal columns.

Question 2

Pause 5s

If we multiply 6.2 by 100, do the digits move or does the decimal point move?

After thinking

The digits move two places left in value. The point stays as the place-value marker.

Excellent. Thinking about digit movement prevents later mistakes.

Question 3

Pause 5s

Why does 25% match one quarter?

After thinking

25% means 25 out of 100, and 25/100 simplifies to 1/4.

Great connection between percentages and fractions.

Deep structure

What children discover

Children discover that decimals and percentages are extensions of place value and parts of a whole.

Common mistake

Children may move the decimal point mechanically instead of understanding that digits change place value.

Future connection

Decimals and percentages prepare students for standard form, interest, statistics, probability and calculator checks.

Standard formPercentage changeStatisticsProbability

Animated demonstration

See the maths move

Decimal digits slide across tenths and hundredths columns, then a hundred square fills to show equivalent percentages.

Decimal digits slide through place-value columns and a hundred grid fills to connect percent with parts out of 100.
HundredsTensOnesTenthsHundredths
.620.
25%25 out of 100

Guided examples

Decimal subtraction

Find 8.4 - 2.76.

  1. 1.Write 8.4 as 8.40 so the columns match.
  2. 2.Subtract hundredths, then tenths, then ones.
  3. 3.Exchange from the ones if needed.
Answer: 5.64

Divide by 100

Find 73.5 รท 100.

  1. 1.Dividing by 100 moves every digit two places right.
  2. 2.Use zero as a placeholder if needed.
Answer: 0.735

Interactive practice

Try it now

For each decimal calculation, say the column names before writing the answer.

0/3 correct

Find 4.8 + 3.65.

Find 6.2 x 100.

Which fraction matches 25%?

Review

Show where the decimal point should sit when writing 6.2 + 0.58.

Show how 0.25, 25% and 1/4 describe the same amount.

Parent signal

The common error is moving the decimal point instead of thinking about digit place value.

Great work. You are connecting number forms like a mathematician.