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Column multiplication is a classic technique taught in schools, but when decimals are involved, many students start to feel unsure. As a maths tutor, I see this confusion often—but with a clear method and a bit of practice, multiplying decimals using the column method becomes straightforward. Let’s walk through the process together!
What Is Column Multiplication?
Column multiplication, sometimes called long multiplication, is a way of multiplying numbers by lining them up in columns and multiplying each digit in turn. It’s a reliable, step-by-step method that works for whole numbers and decimals alike.
The Steps for Multiplying Decimals
Step 1: Ignore the Decimal Points (for Now)
Write the numbers without their decimal points and set up your column multiplication as if you’re working with whole numbers.
Step 2: Multiply as Usual
Carry out the multiplication just as you would for whole numbers, aligning your digits and adding up the partial products.
Step 3: Count the Decimal Places
Count the total number of decimal places in both of your original numbers.
Step 4: Place the Decimal Point
In your answer, count from the right and place the decimal point so that your product has the same number of decimal places as the total you counted in Step 3.
An Example
Let’s multiply : 4.2 \times 3.6
Ignore the decimals: 42 \times 36
Multiply using the column method:
Count decimal places:
4.2 has 1 decimal place, 3.6 has 1 decimal place, so total is 2 decimal places.
Place the decimal point:
1512 \rightarrow 15.12 (move decimal 2 places from the right).
Final Answer:
4.2 \times 3.6 = 15.12Tips from a Maths Tutor
- Line up the digits carefully when multiplying.
- Don’t forget to count the decimal places before writing your final answer.
- Practice with different numbers—the method is always the same!
- If you’re ever unsure, estimate the answer to check if your decimal point is in the right place.
Conclusion
Column multiplication with decimals may seem tricky at first, but once you break it down into steps, it becomes manageable. With guidance from a maths tutor and a bit of practice, you’ll be multiplying decimals confidently in no time. Give it a try with your own examples and see how quickly your skills improve!
