解： 1-3/8-1/10-1/20
=8/8-3/8-1/10-1/20
=(8/8-3/8)-(1/10-1/20)
=5/8-(2/20-1/20)
=5/8-1/20
=25/40-2/40
=23/40
就这样，解法很多的！
1-3/8-1/10-1/20
=5/8-1/10-1/20
=5/8-3/20
19/40
=40/40-15/40-4/40-2/40=40-15-4-2/40=19/40
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