1. The problem statement, all variables and given/known data Here is the question: "In the fall of 2002, a group of scientists at Los Alamos National Laboratory determined that the critical mass of neptunium-237 is about 60 kg. The critical mass of a fissionable material is the minimum amount that must be brought together to start a chain reaction. This element has a density of 19.5 g/cm3 . What would be the radius of a sphere of this material that has a critical mass? r = ______ cm ? " So my answer should be in CM, and I should express my answer using 2 significant figures. 2. Relevant equations Here, equations I used were V = m * d 3. The attempt at a solution What I've done so far: Ok you have Mass = 60 kg D = 19.5g/cm3 I converted 60 kg to 60,000 g because D is in terms of g/cm3 and my final answer is suppose to be cm, so I think this helps simplify it. anyways, I have the equation: V = m * d so (4/3)pi*r3 = 60,000 g * 19.5g/cm3 Okay, I'm unsure what happens when I multiply 60,000 g by 19.5g/cm3 Does my result become 1170000 g2/cm3? or does it remain 1170000 g/cm3 ??? So from what I understand after this, I'm going to get r3 = (3 (result of the above multiplication) ) / 4pi and then take that result and 1/3 it to get my final answer. I'm mostly stuck here on the multiplying 60,000 g by 19.5g/cm3 part. I have the feeling that I understand how to do it but I actually can't do it :/!