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Z.7 Multiply two decimals

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What does it mean to multiply decimals?

Multiplying decimals means finding the product of numbers that include digits to the right of the decimal point. It is just like multiplying whole numbers, but you place the decimal point correctly in the answer.

Example:
  • 0.5 × 0.2 = 0.10
Note

When multiplying decimals, you do not have to line up the decimal points. Instead, count how many digits come after the decimal in both factors, then place the decimal in the product accordingly.

How to multiply decimals step-by-step

Follow these steps to multiply two decimals correctly. The process is similar to whole-number multiplication, with an extra step at the end to place the decimal point.

Steps:
  • Step 1: Ignore the decimal points and multiply the numbers as if they were whole numbers.
  • Step 2: Count the total number of digits to the right of the decimal in both factors.
  • Step 3: Place the decimal point in the product so that it has the same total number of decimal places.
Note

Be careful when counting decimal places—this determines where the decimal point goes in your final answer.

Example: Multiplying two decimals

Let’s multiply 3.2 × 1.5 using the steps we just learned.

Worked Example:
  • Ignore the decimals and multiply 32 × 15 = 480
  • There is one decimal place in 3.2 and one in 1.5. Together, that makes two decimal places.
  • Place the decimal in the product: 4.80 (or simply 4.8)
Note

Multiplying decimals is the same as multiplying whole numbers, but you must place the decimal correctly in your final answer. Double-check your placement!

Multiplying a decimal by a whole number

When one factor is a whole number and the other is a decimal, multiply as you would with whole numbers, then move the decimal point in the product.

Example:
  • 4 × 2.35 = ?
  • Ignore the decimal: 4 × 235 = 940
  • Since 2.35 has two decimal places, the product should also have two.
  • Final answer: 9.40 (or simply 9.4)
Note

Remember that multiplying by a whole number increases the total value. Always check the reasonableness of your answer using estimation.

Multiplying decimals in money situations

Decimals are often used when dealing with money. You might multiply a price by a quantity to find the total cost.

Example:
  • Each notebook costs $2.49. You buy 3 notebooks.
  • 2.49 × 3 = ?
  • Ignore the decimal: 249 × 3 = 747
  • Two digits follow the decimal in 2.49, so the answer becomes 7.47.
  • The total cost is $7.47.
Note

When solving money problems, always include the dollar sign and write your answer to the nearest cent (two decimal places).

Check your answer using estimation

Estimation helps you see if your decimal multiplication result makes sense. Round each number to the nearest whole number and multiply to check.

Example:
  • Estimate 3.6 × 2.8
  • Round 3.6 → 4 and 2.8 → 3
  • 4 × 3 = 12
  • So, your exact answer should be close to 12.
Note

Estimating before and after multiplying helps you catch misplaced decimals or calculation errors.

Example of checking work with place value

You can verify your answer by aligning place values and adding partial products when needed.

Example:

Multiply 2.3 × 1.2

  • Ignore decimals: 23 × 12 =
23
× 12
46
+230
276
  • There are two decimal places in total (one in each factor).
  • Place the decimal two digits from the right → 2.76
Note

Careful, neat work helps ensure your decimal placement and total are correct every time.