Final answer:
The percent uncertainty of the measuring tape is 2.5%.
Step-by-step explanation:
To calculate the percent uncertainty, we need to divide the uncertainty by the measured value and multiply by 100. In this case, the uncertainty is 0.50 cm and the measured value is 20 m, so the percent uncertainty can be calculated as follows:
Percent uncertainty = (0.50 cm / 20 m) * 100 = 0.025 * 100 = 2.5%
Therefore, the percent uncertainty of the measuring tape is 2.5%.