Parts C and D: http://s7.postimg.org/pnq5gry63/image.png Part D of this problem is just like Part C above it. The only difference is the presence of "sin," but that doesn't affect the calculation of percent uncertainty at all. Chapter 1 of my Physics book (Physics: Principles with Applications - Giancoli) says you calculate it by dividing the 0.5 by 71 and multiplying by 100. I used this exact approach for Parts A, B, and C and got the right answers but magically it doesn't seem to work for this last part even though it is the exact same as Parts A, B, and C. Almost seems to be a glitch in the system. The answer should be 0.7, but this doesn't work. I really don't understand what is going on. Thanks for any help with this, guys! Edit: I just randomly punched in values since my awesome professor gives us like 30 attempts for each problem, and wound up discovering the claimed correct answer is 0.3. This makes absolutely no sense and does not equate with the method used to do this problem. I have no idea how one would arrive at 0.3 as the answer. So confused, probably Mastering Physics shenanigans, already reported to professor.