.1) A fictitious element X is composed of 20 percent of the isotope X-50, 15 percent of the isotope X-51, and 65 percent of the isotope X-52. Calculate the relative atomic mass of element X. * 2)Calculate the relative atomic mass of silicon if the three silicon isotopes have mass and relative abundances of 27.9769 (92.2297%), 28.9765 (4.6832%) and 29.9738 (3.0872%). *