Work through the examples below, then open Online Calculator to check your own numbers and practice the skill.
Decimal multiplication method
First ignore the decimal points and multiply the digits as whole numbers. Then count the total decimal places in both original factors and place that many digits after the point in the product.
For 2.4 × 1.5, compute 24 × 15 = 360. The factors each have one digit after the point, for two decimal places altogether. So the result is 3.60 = 3.6.
Multiplication examples
| Problem | Answer | Check |
|---|---|---|
| 1.2 × 0.3 | 0.36 | 12 × 3 = 36; two decimal places |
| 0.05 × 0.2 | 0.01 | 5 × 2 = 10; three decimal places |
| 12.5 × 4 | 50 | 125 × 4 = 500; one decimal place |
| 0.6 × 0.6 | 0.36 | 6 × 6 = 36; two decimal places |
A quick estimate can reveal mistakes. Since 2.4 × 1.5 is a little more than 2 × 1.5, an answer such as 36 would clearly be wrong.
Dividing when the divisor is a decimal
To divide by a decimal, multiply the dividend and divisor by the same power of ten until the divisor becomes a whole number. This does not change the quotient.
For 4.8 ÷ 0.6, multiply both numbers by ten: 48 ÷ 6 = 8. For 2.25 ÷ 0.15, multiply both by one hundred: 225 ÷ 15 = 15.
Why dividing by less than one can enlarge a result
Division asks how many equal groups fit. If each group is only half a unit, two groups fit into a unit. Thus 50,000 ÷ 50% = 50,000 ÷ 0.5 = 100,000.
This is not an error: dividing by 0.5 doubles a positive number. In contrast, multiplying by 0.5 halves it. Do not confuse the two operations when using a calculator’s percent key.
Practice and checked answers
Calculate 0.4 × 0.25, 6.3 ÷ 0.7, and 0.012 × 10. Predict whether the first answer will be larger or smaller than 0.4.
Answers: 0.1, 9, and 0.12. The first answer is smaller because multiplying by 0.25 means taking one quarter of a quantity.
Precision and repeating results
Some decimal divisions never end: 1 ÷ 3 = 0.3333… . A calculator shows an approximation using its available display precision. Round only as far as the question requires. Avoid copying long floating-point tails into reports when a shorter, clearly labeled rounded result is more useful.
Frequently asked questions
What is 1.2 × 0.3?
0.36, because 12 × 3 = 36 and the two factors contain two decimal places in total.
What is 4.8 ÷ 0.6?
8. Multiply both values by ten to get the equivalent division 48 ÷ 6.
Can dividing by 0.5 increase the number?
Yes. Dividing by 0.5 is equivalent to multiplying by two.
Use Online Calculator to verify a new example, then try the related practice activities.