一根绳子,用去80%,又接上2o米,这时绳子的长度是原来总长度的60%,这根绳子原来长多少米?

问题描述:

一根绳子,用去80%,又接上2o米,这时绳子的长度是原来总长度的60%,这根绳子原来长多少米?

20÷[ 60%-(1-80%)]
=20÷40%
=50(米)