a) 5.16 - 18.9 = 80 - 162 = -82
b) 27.18 - 27.12 = 27.(18-12) = 27.6 = 162
c) 39.213 + 87.39 = 39.(213+87) = 39.300 = 11700
d) 180 - [130-(82-40)] = 180 - ( 130 - 42 ) = 180 - 88 = 92
e) 12 : {390:[500-(125+35.7)]}
= 12 : {390:[500-(125+245)]}
= 12 : {390:[500-370]}
= 12 : ( 390 : 130 )
= 12 : 3
= 4