速算及巧算

原式=
1
-------------------------------------
24×35×46＋35×46×57＋46×57×68
----------------------------------
35×46×57

1
= ----------------
24 68
---- +1 + ----
57 35

1 1995 665
= -------- = ---- = -----
6711 6711 2237
----
1995

除数被除数倒过来之后再求倒数即可