If a number is about 400. What is the least it can be? What is the greatest it could be? Show your answers in pictures

If you are estimating to the nearest hundred, then the answer is between 351 and 450. If it's 350 or less, it'd be about 300. If it's 451 or more, it'd be about 500.

250 300 350 400 450 500 550

--|--------|--------|

**-------|--------**|--------|--------|-- | about 300 | about 400
| about 500 |

On the other hand, if you're estimating to the nearest 10 (such as 390, 400, 410, etc.) rather than the nearest 100, then any number between 396 and 405 would be "about 400". Otherwise it would be "about" 390 or 410.