relative atomic mass of an element ???? A sample of neon was found to cotain 90.9% of 20Ne, 0.26% of 21Ne, & 8.8% of 22Ne, Calculate the relative atomic mass of neon. this is what i'v done so far (90.9x 20)+ (0.26x21)+(8.8x22)= 2017/? i dont know what to devide it by ??? I'm not given a mass spectra? P.s. why r relative atomic masses for some elements not whole numbers, is it because they r isotopes????