The weight ratio of two barrels of oil, A and B, is 2:5. If the oil in barrel B is reduced by 1 kg, how many kilograms of oil in barrel A should be reduced in order to keep the ratio unchanged.
甲、乙两桶油的重量比是2：5，乙桶油如果减少1千克，要使比值不变，甲桶油应减少多少千克．
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<result>2/5 = around 0.4</result>