40% of a barrel of oil is used for the first time, and 8 kg is used for the second time. At this time, there is still (1/5) in the barrel. How many kilograms does the barrel of oil weigh?
一桶油，第一次用去40%，第二次用去8千克，这时桶内还剩(1/5)，原来这桶油重多少千克？
<result>20</result>