Question

脱式计算【能简便的要简便】①2-[1/5+(2/5-5/7)]②（2.5-2.5*0.4）÷4速度啊！！

Answer 1

①2-[1/5+(2/5-5/7)]
=2-1/5-2/5+5/7
=7/5+5/7
=49/35+25/35
=74/35;
②（2.5-2.5*0.4）÷4速度啊！！
=2.5×(1-0.4)÷4
=2.5×0.15
=0.375
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Answer 2

①2-[1/5+(2/5-5/7)]
= 2- (1/5+2/5-5/7)
= 2 - 3/5 +5/7
= (70-21+25) /35
= 74 / 35

②（2.5-2.5*0.4）÷4
= 2.5x(1-0.4) /4
= 2.5 x 0.6 /4
= 1.5/4
= 3/16