Q. What are the rules used for round off numbers?

1. If the digit to the instantaneous right of the last significant figure is less than five don't change the last significant figure.

2. If the digit to the instantaneous right of the last significant figure is greater than five round up the last significant figure.

3. If the digit to the instantaneous right of the last significant figure is equal to five and is followed by a nonzero digit round up the last significant figure.

4. If the digit to the instantaneous right of the last significant figure is equal to five and isn't followed by a nonzero digit look at the last significant figure. If it is an odd digit round it up and if it is an even digit don't round up.

Whether you are adding or subtracting or multiplying or dividing you must always report your answer so that it has the same number of significant figures as the measurement with the fewest significant figures.