一根绳子用去2/5,还剩2/5米,这根绳子长多少米?用去多少米?

问题描述:

一根绳子用去2/5,还剩2/5米,这根绳子长多少米?用去多少米?

绳子长:2/5÷(1-2/5)=2/3米
用去:2/3×2/5=4/15米