svetazuna а)
1 5/7 : 1 1/7 = 12/7 : 8/7 = 12/7 * 7/8 = 12/8 = 3/2 = 1 1/2,
б)
3 1/5 : 2 2/15 = 16/5 : 32/15 = 16/5 * 15/32 = 3/2 = 1 1/2,
в)
5 2/3 : 1/3 - 1 7/12 * 6 = 
17/3 * 3 - 19/12 * 6 = 
17 - 19/2 = 
17 - 9 1/2 = 7 1/2

kindgirl999 1 5/7:1 1/7=12/7:8/7=12/7*7/8=3/2=1 1/2
3 1/5:2=16/5*1/2=8/5=1 3/5
5 2/3:1 7/12=17/3:19/12=17/3*12/19= 68/19=3 11/19