A good-quality measuring tape can be off by 0.50 cm over a distance of 20 m. what is its percent uncertainty?

The percent uncertainty can be calculated by the uncertainty divided by the total measure. That is,

Percentage uncertainty = uncertainty / reading

Percentage uncertainty = (0.5 cm * 1 m / 100 cm) / 20 m) * 100

Percentage uncertainty=0.025%

Therefore, the percent uncertainty is 0.025%.