Primary 4 Four Operations of Decimals Study Guide
Primary 4 decimal operations in four short steps: adding and subtracting, multiplying, dividing and rounding, then two purchases problems. Each step has something to tap through, and worked examples and a five-question check come after.
Start here
How do you add, subtract, multiply and divide decimals?
Keep the decimal point in its column.
Your child works with decimals in columns, the same way as with whole numbers. The decimal point decides which column holds ones, tenths and hundredths. So in every operation the point stays lined up, and the answer's point goes straight below or above it.
In this chapter, your child learns to:
- add and subtract decimals with up to 2 decimal places;
- multiply a decimal by a 1-digit whole number;
- divide a decimal or a whole number by a 1-digit number;
- round a quotient to the number of decimal places asked for;
- find one item's price from two purchases.
Step 1
Adding and subtracting decimals
Line up the points, then match the places. Write the numbers so the decimal points sit in one column. If one number has fewer decimal places, write a zero at the end: 6.4 is the same as 6.40. Then work from the hundredths, as with whole numbers, renaming 10 hundredths as 1 tenth, or 1 one as 10 tenths, when needed.
Tap Next step
What is 5.3 − 1.76?
Step 2
Multiplying decimals by a whole number
Start at the hundredths; the point drops straight down. Multiply each place by the whole number, starting from the hundredths and moving left. Rename as with whole numbers: 20 tenths is 2 ones. Place the decimal point in the product directly under the point in the decimal. A quick estimate tells your child whether the answer is the right size.
Tap Next step
What is 1.85 × 6?
Step 3
Dividing decimals and rounding the quotient
Point above the point, then keep sharing. Put the decimal point in the quotient directly above the point being divided. Divide the ones, then the tenths, then the hundredths. When something is left over, append a zero: 2 tenths become 20 hundredths, so the sharing can go on. Stop when nothing is left, or one place beyond the rounding asked for, then round.
Tap Next step
Find 7.8 ÷ 4.
Step 4
Two purchases problems without algebra
Make one item's count match, then compare. Two shopping lists hold the same two items. If one item has the same count in both, the extra items explain the extra cost. If not, repeat a whole purchase, doubling every count and the total, until one count matches. Divide the extra cost by the number of extra items to find one item's price.
Tap Next step
1 bag and 2 hats cost $14.60. 1 bag and 5 hats cost $26.30. How much is 1 hat?
Primary 4 decimal operations questions, worked step by stepWork each one on paper first. A hint is there if you need it, and the working opens one line per tap.
Mei Ling had $20. She bought a book for $8.65 and a pen for $2.90. How much money did she have left?
- Spent: 8.65 + 2.90 = $11.55.
- Write 20 as 20.00, so both amounts have hundredths.
- Left: 20.00 − 11.55 = $8.45.
A bag of rice has a mass of 1.35 kg. What is the total mass of 6 such bags?
- Hundredths: 5 × 6 = 30 hundredths. Write 0, rename 3 tenths.
- Tenths: 3 × 6 + 3 = 21 tenths. Write 1, rename 2 ones.
- Ones: 1 × 6 + 2 = 8 ones. 1.35 × 6 = 8.10.
A ribbon 5 m long is cut into 3 equal pieces. How long is each piece? Give your answer in metres, correct to 2 decimal places.
- 5 ÷ 3 = 1, with 2 ones left.
- Append zeros: 20 tenths ÷ 3 = 6 with 2 left, and the same again for hundredths and thousandths: 1.666.
- The thousandths digit is 6, which is 5 or more, so round up: 1.67.
2 pencils and 1 eraser cost $2.30. 2 pencils and 4 erasers cost $4.40. Find the cost of 1 pencil.
- 3 extra erasers: 4.40 − 2.30 = $2.10.
- 1 eraser: 2.10 ÷ 3 = $0.70.
- 2 pencils: 2.30 − 0.70 = $1.60.
- 1 pencil: 1.60 ÷ 2 = $0.80.
Siti paid $13.50 for 1 file and 3 pens. Ravi paid $33.60 for 3 files and 4 pens. How much would 2 files and 2 pens cost?
- 3 × Siti's purchase: 3 files + 9 pens = 3 × 13.50 = $40.50.
- 5 extra pens: 40.50 − 33.60 = $6.90, so 1 pen = 6.90 ÷ 5 = $1.38.
- 1 file: 13.50 − 3 × 1.38 = 13.50 − 4.14 = $9.36.
- 2 files + 2 pens: 2 × 9.36 + 2 × 1.38 = 18.72 + 2.76 = $21.48.
Step 5
Check yourself
Five quick questions across the four steps. Answers are not stored; each one links to the practice set that fits.
1. What is 7 − 2.45?
2. What is 4.08 × 5?
3. Find 23 ÷ 4.
4. Find 11 ÷ 6, correct to 1 decimal place.
5. 3 cups and 2 plates cost $10.00. 3 cups and 5 plates cost $16.90. How much is 1 plate?
Getting the most from this guide. Sit beside your child with paper and a pencil. Before each tap of Next step, ask what will be written in the highlighted column, then tap to compare. Saying "tenths" and "hundredths" aloud keeps the places clear. Each step takes about five minutes.
For two purchases problems, ask your child to say which item has the same count in both lists before any subtraction. Afterwards, multiply the prices back into both purchases: if both totals come out right, the answer is right.
More study guides
P4 Four Operations of Decimals lessons and practice
4 lesson videos and 36 questions across four subtopics, from Basic to Challenge, each with a worked solution.
Watch and practise →