Why would or wouldn't the sum of 5.7cm and 6.2cm have to be rounded?

The sum of 5.7 cm and 6.2 cm would typically need to be rounded because it is the result of adding two measurements, each with one decimal place. When adding measurements, the result should be rounded to the least precise measurement, which in this case is one decimal place. Thus, the sum of 11.9 cm would remain as is, but if it were to be expressed in a different context requiring rounding, it might be rounded further.