7/12 + 3/4 = 7/12 + 9/12 = 16/12 = 4/3 = 1 1/3,
2/3 + 5/8 = 16/24 + 15/24 = 31/24 = 1 7/24,
8/21 + 5/14 = 16/42 + 15/42 = 31/42,
9/20 + 7/16 = 36/80 + 35/80 = 71/80
1 сут = 24 час = 1440 мин
2 сут = 2880 мин
2880 - 30 = 2850 мин
8=2,2,2
17=1
24=2,2,2,3
НОД ( 1*3) = 3