Decimals x Whole Numbers — Multiply & Divide Pathway
Multiplying decimals by whole numbers
- Ignore the decimal point — multiply as whole numbers.
- Then put the decimal point back in the answer.
- Count how many decimal places were in the question.
- Example: 2.5 x 3 — multiply 25 x 3 = 75, then add the point: 7.5.
Example: 3.4 x 5
- Step 1: Ignore the decimal: 34 x 5 = 170.
- Step 2: There was 1 decimal place in 3.4.
- Step 3: Put 1 decimal place in the answer: 17.0.
- Answer: 3.4 x 5 = 17.
Your turn
- Try: 4.2 x 3.
- Remove decimal: 42 x 3 = 126.
- Original had 1 decimal place.
- Answer: 12.6.
Common Mistakes to Avoid
- Forgetting to put the decimal point back. Count the decimal places in the question and make sure the answer has the same number.
- Putting the decimal point in the wrong place. Count from the right of the answer.
Real-Life Example
A bag of flour weighs 3.4 kg and a baker uses 5 bags. 3.4 x 5: ignore the decimal and do 34 x 5 = 170, then put 1 decimal place back: 17.0 kg.
Extra Support Hints
- Count the decimal places in the question — the answer must have the same total.
- Check by estimating: 3.4 is about 3, and 3 x 5 = 15, so 17 is sensible.