[tex] \frac{1}{28} + \frac{7}{72} + \frac{1}{84} = \frac{18}{504} + \frac{49}{504} + \frac{6}{504}= \frac{73}{504} \\ \\ \frac{1}{8}+ \frac{4}{3} + \frac{9}{2}= \frac{3}{24} + \frac{32}{24} + \frac{108}{24}= \frac{143}{24 } \\ \\ \frac{21}{10}+ \frac{106}{35} + \frac{17}{14} = \frac{147}{70}+ \frac{212}{70} + \frac{85}{70}= \frac{444}{70}(:2)= \frac{222}{35} \\ \\ \frac{7}{120}+ \frac{11}{240} + \frac{1}{400} = \frac{70}{1200} + \frac{55}{1200} + \frac{3}{1200}= \frac{128}{1200} [/tex]
