Use the distributive method to check the product
Split 4 into 3 + 1. Multiplying each part by 21 and adding the partial products is a separate, easy-to-audit route to the same answer.
- 1.21 × 3 = 63.
- 2.21 × 1 = 21.
- 3.63 + 21 = 84.
What is 21 times 4?
21 times 4 is 84.
Worked out below step by step, with a table of related values and a live calculator so you can change the numbers.
Answer
84
21 × 4
Answer
Step-by-step working
- 1. Set up the multiplication: 21 × 4.
- 2. Multiply the two numbers together.
- 3. The answer is 84.
Check it: 84 ÷ 4 = 21, the first number again.
Formula
answer = first number × second number
Multiplication is repeated addition. Swapping the two numbers gives the same product.
Understanding 21 times 4
Multiplication combines 21 equal groups of 4, or 4 equal groups of 21. That repeated scaling gives the product 84.
The operation is useful for totals, repeated quantities, rectangular area and scale factors. Multiplication is commutative, so reversing the two factors does not change the product.
Reasonableness and accuracy checks
- Divide 84 by 21; the quotient should be 4.
- Divide 84 by 4; the quotient should be 21.
- Estimate using nearby round numbers to catch a misplaced decimal or an extra zero.
A second worked example
What is 21 times 5?
21 × 5 = 105
Set up the multiplication: 21 × 5. Multiply the two numbers together. The answer is 105. This uses the same method with different numbers, so it shows how the rule transfers instead of only repeating the original answer.
Product insight for 21 × 4
The product is 84, which is even because both factors are whole numbers and their parity determines the product. Reversing the factors to 4 × 21 must give exactly the same product, which provides a simple structural check before relying on the result.
Where multiplication is useful
Multiplication handles repeated quantities such as items per pack, hours at a rate, rows and columns, area factors and scaled measurements. A distributive check is especially useful when the factors are large enough that a single mental multiplication is error-prone.
Common mistakes to avoid
- Losing a decimal place when one or both factors contain decimals.
- Adding the factors instead of multiplying them when interpreting repeated groups.
- Skipping a rough magnitude check, which can allow an extra zero or a misplaced decimal to go unnoticed.
Questions about this calculation
Is there another way to check What is 21 times 4?
Split 4 into 3 + 1. Multiplying each part by 21 and adding the partial products is a separate, easy-to-audit route to the same answer. 21 × 3 = 63. 21 × 1 = 21. 63 + 21 = 84.
What is the most common mistake with What is 21 times 4?
Losing a decimal place when one or both factors contain decimals. After correcting that setup, verify the result independently: Check it: 84 ÷ 4 = 21, the first number again.
Can I use the same method with different numbers?
Yes. What is 21 times 5? Set up the multiplication: 21 × 5. Multiply the two numbers together. The answer is 105. This uses the same method with different numbers, so it shows how the rule transfers instead of only repeating the original answer. The live calculator above lets you replace both inputs and recalculate without changing the underlying method.
How can I tell whether 84 is reasonable here?
The product is 84, which is even because both factors are whole numbers and their parity determines the product. Reversing the factors to 4 × 21 must give exactly the same product, which provides a simple structural check before relying on the result. Use that scale or ratio check together with the reverse calculation before reusing the result in another calculation.
21 multiplied by other numbers
| Multiplier | 21 × multiplier |
|---|---|
| 1 | 21 |
| 2 | 42 |
| 3 | 63 |
| 4 | 84 |
| 5 | 105 |
| 6 | 126 |
| 8 | 168 |
| 10 | 210 |
| 12 | 252 |