#1)-2
#2)5/6 * 3/5 = 1/2( или 0,5)
8/9 : 4/3 = 8/9 * 3/4 =2/3
5/3 * 6/25 : 8/5 = 2/5 : 8/5= 2/5 * 5/8 =2/8= 1/4
#3)2/3:7/12*(4-1 7/8)+1 5/6=
=2/3*12/7*(3 7/8)+1 5/6=
=8/7*3 7/8+1 5/6=
=8/7*31/8+1 5/6=
=31/7+1 5/6=
=3 3/7 + 1 5/6=
=3 18/42 + 1 35/42=
=4 53/42= 5 11/42