1： ⑴ A ⑵ A ⑶B
2： ⑴ 7 42 28
⑵ 5/4
⑶ 31
3： 8/3 7/12 8/5 4/25
4: (3/4－2/3)÷1/5 (3/8+2/17)×8+1/17
=1/12×5 =3/8X8+2/17X2+1/17
=5/12 =3+(16/17+1/17)
=3+1
=4
4/5x7/8+7/8÷5 (1－8/15x3/4)÷3/5
=4/5x7/8+7/8x1/5 =(1－2/5)3/5
=7/8x(4/5+1/5) =3/5÷3/5
=7/8x1 =1
=7/8
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