*Lời giải :
a) 1 3/5 . `0,5^2` - 3 + (8/5 - 1 19/60) : 1 23/24
= 8/5 . 1/4 - 3 + (8/5 - 79/60) : 47/24
= 9/20 - 3 + 17/60 : 47/24
= 9/20 - 3 + 34/235
= -51/20 + 34/235
= -2261/940
b) -7/8 . 5/9 - 4/9 . 7/8 + 5 7/8
= 7/8 . (-5/7 - 4/9) + 47/8
= 7/8 . (-1) + 47/8
= -7/8 + 47/8
= 5
c) 50% . 1 1/3 . 10 . 7/35 . 0,75
= 1/2 . 4/3 . 10 . 7/35 . 3/4
= 1 . 4 . 10 . 7 . 3/2 . 3 . 1 . 35 . 4
= 1
d) 0,25 . 1 3/5 . `5^2/4` : -4/7
= 1/4 . 8/5 . 25/4 . -7/4
= 1 . 8 . 25 . -7/4 . 5 . 4 . 4
= -35/8