有两根绳子，如果两根绳子都剪掉同样的长度，剩下的长度比为2：1，如果两根绳子再剪掉与上次剪掉的同样长度，剩下的长度比是3：1．求原来两绳子的长度比？
口算：+= 3﹣2= 1÷1= 7×÷7×= 5÷5=×1.2=×1=（+）×20=
直接写得数． 4÷40%=×= 20×5.5=（+）×4=﹣= 2.9+3.4= 0.1÷0.01= 6﹣﹣=÷3= 6×=÷= 1÷﹣÷1=
直接写出得数+=×= 1﹣20%﹣= 4×==+25%= 3﹣==
直接写得数．= 4﹣1.63======== 27×5%=%==
直接写得数+=﹣=×=×=×÷×=+=×0+3= 3+1.75=÷=（+）×=
+
= 3﹣2
= 1
÷1= 7×
÷5=
×1.2=
×1
=（
+
）×20=
×
= 20×5.5=（
+
）×4=
﹣
= 2.9+3.4= 0.1÷0.01= 6﹣
﹣
=
÷3= 6×
=
÷
= 1÷
﹣
÷1=
+
=
×
= 1﹣20%﹣
= 4×
=
=
+25%= 3﹣
=
=
= 4﹣1.63=
=
=
=
=
=
=
= 27×5%=
%=
=
+
=
﹣
=
×
=
×
=
×
÷
=
=
×0+3= 3
+1.75=
÷
=（
+
）×
=
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