Square of 20
20 squared equals 400. Squares appear in area calculations, the Pythagorean theorem, and statistics (variance uses squared distances).
Squares obey quiet rules. Divided by 9, a square only ever leaves 0, 1, 4 or 7 — 4 here. On the last digit, squares end only in 0, 1, 4, 5, 6 or 9, and 0 fits. Between its neighbors, 361 sits 39 below and 441 sits 41 above — the square ladder widens by exactly two at every step. Double the base and the square quadruples: 40² = 1600, which is 4 × 400. Two anchors most worth memorizing in this range are 12² = 144 and 15² = 225 — the odd-step rule above is why knowing them pays off, because from any anchor the next square is one step along this page's ladder.
| Expression | Value |
|---|---|
| 20² | 400 |
Frequently asked questions
What is 20 squared?
20 squared is 400, because 20 × 20 = 400. The exponent 2 is why it is written 20².
What is 21 squared, next to 20²?
21² = 441, which is 41 more than 20² = 400. Each step up adds double the base plus one.
Where do squares show up in real problems?
Area of a square with side 20, distance in the Pythagorean theorem, and variance in statistics all use squared values.