一瓶牛奶先喝了1/5,又喝了剩余的1/5,这时牛奶剩余4/5千克,问原来牛��

Answer 1

4/5÷{1-[1/5+1/5*(1-1/5)]}
=4/5÷[1-(1/5+1/5*4/5)]
=4/5÷[1-(1/5+4/25)]
=4/5÷(1-9/25)
=4/5÷16/25
=4/5×25/16
=5/4 千克