I am asked "What is the area and it's approximate uncertainty of a circle of radius 3.8x10^4 cm?" Now finding the area is easy. In my text it says that when you aren't GIVEN an uncertainty, you can assume it is a reasonable figure in the last digit, so in this problem I am assuming the original value is 32,000 cm +/- 5 cm. So far so good... Now, how do I find the percent uncertainty of my final answer? Because I know the percent uncertainty in my 32,000 cm figure, but how does this come into play after squaring it and multiplying it by pi?