a) 80 – 35 = 80 – 30 – 5 = 50 – 5 = 45

39 – 27 = 39 – 20 – 7 = 19 – 7 = 12

61 – 16 = 61 – 10 – 6 = 51 – 6 = 51 – 1 – 5 = 45

b ) 91 – 79 = 91 – 70 – 9 = 21 – 9 = 21 – 1 – 8 = 20 – 8 = 12

83 – 14 = 83 – 10 – 4 = 73 – 4 = 69

54 – 28 = 54 – 20 – 8 = 34 – 8 = 26

c) 

970 –