Final answer:
The percent error for Diego's measurement is approximately 8.7%.
Step-by-step explanation:
To calculate the percent error, we use the formula:
Percent Error = (|Measured Value - Actual Value| / Actual Value) x 100%
For this problem, the measured value is 21 cm and the actual value is 23 cm. Plugging these values into the formula, we get:
Percent Error = (|21 - 23| / 23) x 100%
Percent Error = (2 / 23) x 100%
Percent Error ≈ 8.7% (rounded to one decimal place)
Therefore, the option closest to the percent error for Diego's measurement is B. 8.7%.