a) 3/4 . 16/9 - 7/5 : -21/20
= 4/3 - 7/5 . 20/-21
= 4/3 - (-4/3)
= 12/9 - -12/9
= 8/3
b) 2 1/3 - 1/3 . (-3/2 + (2/3 + 0,4 . 5))
= 7/3 - 1/3 . (-3/2 + (2/3 + 2/5 . 5))
= 7/3 - 1/3 . (-3/2 + 8/3)
= 7/3 - 1/3 . 7/6
= 7/3 - 7/18
= 126/54 - 21/54
= 35/18
c) (20 + 9 1/4) : 2 1/4
= (20 + 37/4) : 9/4
= 117/4 : 9/4
= 117/4 . 4/9
= 13
d) (6 - 2 4/5) . 3 1/8 - 1 3/5 : 1/4
= (6 - 14/5) . 25/8 - 8/5 : 1/4
= 16/5 . 25/8 - 32/5
= 10 - 32/5
= 18/5
