College Physics Problem 1.20

(a) A person’s blood pressure is measured to be 120±2 mmHg. What is its percent uncertainty?
(b) Assuming the same percent uncertainty, what is the uncertainty in a blood pressure measurement of 80 mmHg?


a) The percent uncertainty is computed as

% uncertainty=frac{2  mmHg}{120  mmHg}times 100%=1.7%


b) The uncertainty in the blood pressure is

delta_{bp}=frac{1.7%}{100%}times 80  mmHg=1.3  mmHg