Final answer:
The error interval for N when it is truncated to one digit resulting in 8 is from 7.5 to 8.5, excluding 8.5.
Step-by-step explanation:
If Millie truncates the number N to 1 digit and the result is 8, the error interval for N is the range of numbers that could round to 8 when truncated to one digit. The smallest number that would round up to 8 is 7.5, and the smallest number that would round up to 9 is 8.5. Therefore, if N is truncated to 8, the error interval of N would be from 7.5 to 8.5, not including 8.5 since 8.5 would round to 9.