When a question involves upper and lower bounds, you might need to give our answer to an appropriate degree of accuracy
You can use this strategy
Calculate the lower bound for the answer
Calculate the upper bound for the answer
Choose the most accurate value that both bounds would round to
Problem solved
Choose an answer that both bounds will round to
Check 2 significant figures
Examiners report
When you are told that values in the question have been rounded, there is a good chance that you will have to work with bound, you can score some marks on these questions just by writing down the upper and lower bounds of the rounded values
Error intervals
If you need to write an error interval, you should use inequalities to show the lower and upper bounds for a rounded value