Long Multiplication: 21 × 8
What is 21 × 8?
Answer
21 × 8 and 8 × 21 are the same product — the order of the factors never changes the answer, only the working. Below, 21 is multiplied by 8 in a column, digit by digit.
21 × 8 in a Column
The multiplicand goes on top, the multiplier underneath, both aligned on the right. The multiplier has a single digit, so there is one partial product and the answer goes straight under the line.
| 2 | 1 | ||
| × | 8 | ||
| 1 | 6 | 8 |
Step-by-Step Solution
Step 1: Multiply the multiplicand by the last digit of the multiplier, 8: 21 × 8 = 168.
- 1 × 8 = 8. Write 8.
- 2 × 8 = 16. Write 6 and carry 1.
- No digits are left, so the carried 1 is written in front: the partial product is 168.
21 × 8
=168
Check It, and What It Is Not
Check by dividing back. Multiplication and division undo each other, so 168 ÷ 8 = 21 must come out exactly, with no remainder.
Fractions are a different calculation. Both factors here are whole numbers; for 2/3 or 2 3/4 use the fraction multiplication calculator, which multiplies numerators and denominators separately.
21 × 8 is a number, not an area. If those are the sides of a room in feet, the answer is 168 square feet — the same arithmetic, a different question, and it is answered by the square footage calculator.
Related Calculations
See Also
- Long Division Calculator - Step-by-step long division with detailed explanation
- Multiplying Fractions Calculator - Multiply fractions, mixed numbers and whole numbers step by step
- Factors of a Number - List all Factors and Factor Pairs of a Number
- Greatest Common Factor - Find the Greatest Common Factor (GCF) of two numbers
- Least Common Multiple - Find the Least Common Multiple (LCM) of two numbers
<a href="https://calculat.io/en/number/long-multiplication/21--8">21 × 8 = 168 - Long Multiplication - Calculatio</a>