Решение:

• a) $$rac{420}{1400} = \frac{42}{140} = \frac{21}{70} = \frac{3}{10}$$
• б) $$rac{2079}{1089} = \frac{693}{363} = \frac{231}{121} = \frac{21}{11}$$
• в) $$rac{312}{468} = \frac{156}{234} = \frac{78}{117} = \frac{26}{39} = \frac{2}{3}$$
• г) $$rac{2695}{4235} = \frac{539}{847} = \frac{77}{121} = \frac{7}{11}$$
• д) $$rac{312}{2079} = \frac{104}{693} = \frac{8}{53}$$
• e) $$rac{1400}{4235} = \frac{280}{847} = \frac{40}{121}$$