Final answer:
To prevent Excel from rounding 16-digit numbers, change the cell format to Text before entering the number. For computations, perform calculations in a single step to ensure only the final result is rounded.
Step-by-step explanation:
To stop Excel from rounding 16-digit numbers, one method is to change the cell format to Text before typing or pasting the number into the cell. This will prevent Excel from treating the number like a numerical value and rounding it. If it's important to perform mathematical calculations, you should keep calculations within one step when possible to avoid rounding errors. For instance, rather than rounding off numbers during intermediate steps of a calculation, you can calculate the whole expression in a single step, which ensures that only the final result is rounded off according to significant figures rules. This approach avoids the potential for rounding errors that can occur if intermediate results are rounded before the final calculation.
For example, if you're dealing with the expression (13.2 + 12.252) x (1.35 x 2.1), instead of rounding intermediate results, perform the calculation in one go: 25.452 x 2.835 = 72.15642, which is rounded to 72 to match the number of significant figures in the original data. This method will give you a more accurate result than if intermediate rounding had been applied, which could have led to the incorrect final answer of 71.