Two lengths, a and b, are measured to be 51+/-1cm and 49+/-1cm respectively. In which of the following is the percentage uncertainty the largest? A a+b B a-b C a x b D a/b The answer should be b but I can't figure out why. I know that for / and x you add the percentage errors so if the error is approx 2% then each of C and D have errors of 4% of their answers ie C 51 x 49 = 2499 and 4% is ~100 D 51/49 = 1 and 4 % is 0.04 I think that for + and - you add absolute uncertainties ie 0,02 + 0.02 = 0.04 ie A 51 + 49 = 100 and 100 x 0.04 = 4 B 51 - 49 = 2 and 2 x 0.04 = 0.08 But that makes C the largest error. What am I missing here? It's supposed to be multiple choice, non calculator so I'm probably overthinking it?