The length of a wall is 9 metres to the nearest metre. Complete the error interval for the length of the wall.

When a measurement is given to a certain degree of accuracy, there is a range of possible actual values. This range is called the error interval. The length is 9 metres to the nearest metre. 1. Find the degree of accuracy: It is 1 metre. 2. Halve this value: 1 ÷ 2 = 0.5 metres. 3. The lower bound is the smallest value that would round up to 9. We find this by subtracting 0.5 from the measurement: Lower bound = 9 - 0.5 = 8.5 m. 4. The upper bound is the smallest value that would round up to the *next* measurement (10). We find this by adding 0.5 to the measurement: Upper bound = 9 + 0.5 = 9.5 m. The error interval is written as: Lower Bound ≤ actual length < Upper Bound. The actual length can be equal to the lower bound (8.5 would round up to 9), but it must be strictly less than the upper bound (9.5 would round up to 10). So, the error interval is: 8.5 ≤ length < 9.5.