Key learning points

1. When given a rounded number you can say what the biggest and smallest values of the unrounded number could have been .
2. You can use a ≤ x < b notation to express the range of values the unrounded number could have taken.
3. You can use those values in your estimate to see what your biggest and smallest answers could have been.
4. The range of possible answers is the error interval.

Keywords

• Upper bound - The upper bound for a rounded number is the smallest value that would round up to the next rounded value.

• Lower bound - The lower bound for a rounded number is the smallest value that the number could have taken prior to being rounded.

• Error interval - An error interval for a number x shows the range of possible values of x. It is written as an inequality a ≤ x < b

Common misconception