1.第一天看了全书的1\12=2/24
第二天比第一天多看了全书的1\24
第二天看了全书的2/24+1/24=3/24
现在这本书还有几分之几没有看
=1-(2/24+3/24)
=1-5/24
=19/24
2.脱式
(1)3\8+5\6-7\12
=9/24+20/24-14/24
=29/24-14/24
=15/24
=5/8
(2)9\20+4\15+1\6
=54/120+32/120+20/120
=106/120
=53/60
(3)3\5+7\10-8\15
=18/30+21/30-16/30
=39/30-16/30
=23/30
(4)3\7-8\21+9\14
=18/42-16/42+27/42
=2/42+27/42
=29/42
3.简便
(1)3\4+9\20+6\20
=3/4+15/20
=3/4+3/4
=6/4
=1.5
(2)2\5-1\2+3\5
=2/5+3/5-1/2
=1-1/2
=1/2
(3)5\12-(5\12-2\5)
=5/12-5/12+2/5
=0+2/5
=2/5
(4)23\39+5\13+8\13
=23/39+13/13
=1又23/39