1) 28/35 = (7*4)/(7*5) = 4/5
Ответ: 4/5
2) 8/12 = (4*2)/(4*3) = 2/3
Ответ: 2/3
3) 39/12 = (3*13)/(3*4) = 13/4 = 3 1/4
Ответ: 3 1/4
4) (8*11)/(33*4) = (8*11)/(11*3*4) = (4*2*11)/(11*3*4) = 2/3