20 times 21 is 420. In symbols: 20 × 21 = 420, and 21 × 20 = 420 too.
20 × 21 means adding 20 to itself 21 times: that is 21 copies of 20, which add up to 420.
20, 40, 60, 80, 100, 120, 140, 160, 180, 200, 220, 240, ... (keep going to the 21th multiple). The 21th multiple of 20 is 420.
20 × 21 = 20 × 20 + 20 × 1 = 400 + 20 = 420.
Halve one number and double the other: 20 × 21 = 10 × 42 = 420.
420 ÷ 20 = 21
420 ÷ 21 = 20
420 is even. Prime factorization: 2 × 2 × 3 × 5 × 7.
| Multiplication | Answer |
|---|---|
| 19 × 21 | 399 |
| 21 × 21 | 441 |
| 20 × 20 | 400 |
| 20 × 22 | 440 |
| 20 × 23 | 460 |
| 19 × 20 | 380 |
| 21 × 22 | 462 |
| 18 × 21 | 378 |
Other numbers? Browse the multiplication table, the squares and cubes or the exponent calculator.