a) -0,4= 2 /5 2 1/7= -2 1/7 2/5 = - 5/2 b) 3/5 = 5/3 18=1/18 -5= -1/5 1 5/7=12/7= 7/12 0,2=5/10=1/2=2 -1=-1 4,7=4 7/10= 47/10=10/47