(1)
×9 2
÷5 4
×9 2
5 4
=
×9 2
×5 4
×2 9
5 4
=
9×5×2×5 2×4×9×4
=
;25 16
(2)
÷[10 21
×(1-5 6
)]2 3
=
÷[10 21
×5 6
]1 3
=
÷10 21
5 18
=
;12 7
(3)(68-
)×17 18
1 17
=68×
-1 17
×17 18
1 17
=4-
1 18
=3
.17 18