а) НОК (8;12) = 24
Кратное 8: 8, 16, 24, 32, 40, 48, 56, 64, 72...
Кратное 12: 12, 24, 36,48, 60, 72...
б) НОК (2; 5; 7) = 70
Кратное 2: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72...
Кратное 5: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75 80...
Кратное 7: 7, 14, 21, 28, 35, 42, 49, 56, 63, 70, 77...
в) НОК (2; 4; 7) = 28
Кратное 2: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32...
Кратное 4: 4, 8, 12, 16, 20, 24, 28, 32, 36...
Кратное 7: 7, 14, 21, 28, 35, 42...
2.120+30=150 минут
3.240+5=245 минут
4.420+48=468 минут