a) 51/2 - 4.1/2=51/2 - 4x2+1/2=51/2 - 9/2=42/2=21
b) 31/3 - 2.2/3=31/3 - 8/3=23/3
c) 4 - 21/5=20/5 - 21/5= -1/5
d) 4- (21/3 + 11/3)= 4 - 32/3= 12/3 - 32/3= - 20/3
e) 41/12 - ( 5- 37/12) = 41/12 - ( 60/12-37/12) = 41/12 - 23/12=18/12=3/2
f) 21/5 - [ 4 - ( 31/5 + 3/5) = 21/5 - ( 4 - 34/5)=21/5 - ( 20/5 - 34/5) =
= 21/5 +14/5= 35/5=7