I got this question on a multiple choice test and I couldn't do it. The question was "Calculate the volume of the earth knowing that the mean radius is 6371 km." What I did was multiply 4*pi*6371^3 then divided the answer by 3 but it didn't yield the correct answer. I got the solutions sheet for the test and heres how the teacher solved the problem = 4pi * (6.371 * 10^3)^3 / 3 = 4pi * (6.371)^3 * 10^9 / 3 They're the first two steps of his solution but I'm completely lost. How do you magically get a different answer by using scientific notation? I know the laws of indices but I don't understand how I got a different answer because I didn't use scientific notation to represent 6371 km.