Final answer:
The sum of 2.5 cm, 0.50 cm, and 0.055 cm is 3.055 cm when added, but when rounded to one decimal place based on the least number of decimal places in the provided numbers, the correct answer is 3.1 cm.
Step-by-step explanation:
To add the three numbers 2.5 cm, 0.50 cm, and 0.055 cm with proper significant figures, we must look at the number with the least number of decimal places. Here, 2.5 cm has the fewest decimal places (one), which means our result should also be reported to one decimal place. Adding the numbers gives us 2.5 + 0.50 + 0.055 = 3.055. However, we must round to one decimal place, which results in 3.1 cm.