Final answer:
To calculate the percent of change for Danny's measurement, use the formula: (Actual value - Measured value) / Actual value * 100.
Step-by-step explanation:
The percent of change can be calculated using the formula:
Percent change = (Actual value - Measured value) / Actual value * 100
For Danny's measurement, the actual length of the pen is 23 cm and Danny measured it to be 22 cm. So, the percent of change would be:
Percent change = (23 - 22) / 23 * 100 = 4.34%
Therefore, the closest option to the percent of change for Danny's measurement is 4.3% (option a).