I saw similar types of problems like this using Google search, but none of them answered this question specifically. 1. The problem statement, all variables and given/known data As you eat your way through a bag of chocolate chip cookies, you observe that each cookie is a circular disk with a diameter of 8.5 +/- 0.02 cm and a thickness of 0.050 +/- 0.005 cm. Find the ratio of the diameter to the thickness and the uncertainty in this ratio. 2. Relevant equations 3. The attempt at a solution So what I did was just put 8.50 +/- 0.02 cm divided by 0.050 cm. My answer was : 170 +/- 4cm Their answer was : 170 +/- 20 cm. So I see where they got the 170 from, but I'm not sure why they 20cm is there.