Primary 4 · Number & Algebra
P4 decimals
In P4, place value reaches past the decimal point into tenths, hundredths and thousandths. Your child compares and orders decimals, changes them to fractions and back, rounds them, adds and subtracts them, and multiplies and divides them by a whole number.
- Taught in
- Term 3
- Syllabus
- 6 skills
- Usual slip
- Counts the digits
What your child learns in P4 decimals
Six skills, each with what it looks like on a worksheet.
See the syllabus wording
- notation, representations and place values (tenths, hundredths, thousandths)
- comparing and ordering decimals
- expressing decimals as fractions
- expressing fractions as decimals when the denominator is a factor of 10 or 100
- rounding decimals to the nearest whole number, 1 decimal place, 2 decimal places
- adding and subtracting decimals (up to 2 decimal places)
- multiplying and dividing decimals (up to 2 decimal places) by a 1-digit whole number
- dividing a whole number by a whole number with quotient as a decimal
- rounding answers to a specified degree of accuracy
Tenths, hundredths and thousandths
Place value carries on to the right of the ones. In 0.746, the 7 is 7 tenths, the 4 is 4 hundredths and the 6 is 6 thousandths.
| Point | Value |
|---|---|
| 0.7 | 0.7 |
Compare and order decimals
Line up the decimal points and compare from the left, tenths first, then hundredths. 0.5 is bigger than 0.45, because 5 tenths beat 4 tenths. The number of digits does not matter.
| Number | Ones | Tenths | Hundredths |
|---|---|---|---|
| 0.5 | 0 | 5 | 0 |
| 0.45 | 0 | 4 | 5 |
Decimals and fractions
0.7 is seven tenths and 0.25 is 25 hundredths, or one quarter. To change three quarters into a decimal, make the denominator 100 first: 75 hundredths, which is 0.75.
| Point | Value |
|---|---|
| Point 1 | 0.75 |
Round decimals
Look at the digit just to the right of the place you are rounding to. 5 or more rounds up. 3.46 is 3.5 to 1 decimal place, and 3 to the nearest whole number.
| Point | Value |
|---|---|
| 3.46 | 3.46 |
Add and subtract decimals
Line up the decimal points, fill an empty place with 0, then work from the right as with whole numbers. 7.6 − 2.85 is written 7.60 − 2.85, which is 4.75.
Multiply and divide by a whole number
Work as with whole numbers and keep the decimal point in line: 2.4 × 3 = 7.2. Dividing 9 by 4 gives 2.25, with zeros written after the point to keep going.
Key facts and formulas
- Tenths, hundredths, thousandthsEach place is worth a tenth of the place to its left.the 6 in 2.465 →
Ones . Tenths Hundredths Thousandths 2 . 4 6 5 - Compare and order decimalsLine up the decimal points. Compare the tenths first, then the hundredths: 0.7 is greater than 0.68.
Tenths Hundredths 0.70 7 0 0.68 6 8 - Decimal to fractionWrite it over 10, 100 or 1000, then simplify.
- Fraction to decimalMake the denominator 10 or 100.
- Rounding decimalsLook at the next digit to the right. 5 or more, round up.nearest whole number → 1 decimal place → 2 decimal places →
Point Value 5.374 5.374 - Add or subtract decimalsLine up the decimal points. Fill an empty place with 0.
- × or ÷ by a 1-digit numberWork as with whole numbers. Keep the decimal point in line.
- A whole number ÷ a whole numberWrite zeros after the point to keep dividing. Round the answer when the question asks. 2 decimal places →
Words to know
- Tenths
- The first place after the decimal point. 0.4 is 4 tenths.
- Hundredths
- The second place after the decimal point. 0.04 is 4 hundredths.
- Place value
- What a digit is worth because of where it sits in the number.
- Decimal place
- A place after the decimal point. 3.46 has 2 decimal places.
- Placeholder zero
- A 0 written in an empty place, so 0.5 becomes 0.50.
The sentence that costs the mark
Which is bigger, 0.45 or 0.5?
What the working usually does
digits0.45 vs 0.5=0.45
Compares them like whole numbers: 45 beats 5, so it picks 0.45. But more digits does not mean a bigger number.
What the question asked
tenths0.45 vs 0.5=0.5
Lines the points up and compares the tenths first: 5 tenths beats 4 tenths, so 0.5 is bigger. 0.5 is the same as 0.50.
0.45 does have more digits, and for whole numbers more digits does mean bigger, so the habit transfers. Lining up the decimal points shows 0.5 is 0.50: 5 tenths against 4, settled before the hundredths.
The same P4 decimals question, worked properly
Lah works through it the way she does every question in StudyLah: one step at a time, marking the picture as she goes.
Arrange the decimals 0.36, 0.063 and 0.6 in order, starting with the smallest.
- Line up the decimal points in a place-value chart. With zeros filling the empty places, the numbers are 0.360, 0.063 and 0.600.
- Compare the tenths first, not the number of digits. 0.6 has 6 tenths, 0.36 has 3 tenths and 0.063 has 0 tenths.
- 0 tenths is the least and 6 tenths is the most, so 0.063 is the smallest and 0.6 is the greatest, with 0.36 between them.
- So the order is 0.063, 0.36, 0.6.
Every question in StudyLah comes with a walkthrough like this one.
Try it freeThree quick P4 decimals questions
Try them together, then tap to check.
Question 1
What is the value of the digit 8 in 47.83?
Show answer
Answer0.8. The 8 sits in the tenths place, so it is worth 8 tenths.
Question 2
Convert to a decimal.
Show answer
Answer0.36. Make the denominator 100: = , which is 36 hundredths.
Question 3
What is 5.6 + 13.82, correct to the nearest tenth?
Show answer
Answer19.4. Line up the points, so 5.60 + 13.82 = 19.42. The hundredths digit is 2, so it rounds down.
Helping at home
How to tell it has clicked
Write 0.45 and 0.5 and ask which is bigger. If your child lines up the points, says 0.5 is 0.50 and compares the tenths, they have it. If they say 0.45 because "45 is more than 5", that is the slip.
The money version is the quickest check: would they rather have $0.50 or $0.45? Every child picks the fifty cents, which is the same as saying 0.5 is bigger.
Try this tonight
Use coins. $0.50 against $0.45, even though "45" looks like the bigger number. Ask which they would rather have, then line the two amounts up and count the tenths together: 5 against 4.
Then try pairs like 0.3 and 0.28, or 0.7 and 0.65. Each time, line up the points, fill a zero if one is shorter, and compare from the left.
Before and after P4 decimals
Builds on
Primary 3 FractionsCompares, simplifies, adds and subtracts fractions
Builds on
Primary 3 MoneyAdds and subtracts dollars and cents
You are here
Primary 4 Decimals
Compares decimals place by place
Leads to
Primary 5 DecimalsMoves decimals by 10, 100 and 1000
Leads to
Primary 5 PercentageWrites parts of a whole out of 100
More in Primary 4
Struggling with the working rather than the topic itself? How to help your child with problem sums
See how your child is doing on this topic
StudyLah marks each step separately, so you can see whether it was the setup or the arithmetic that cost the mark.