barrel of oil weighs 5.2 kilograms. After pouring half of the oil, the barrel weighs 2.7 kilograms. How many kilograms of oil are there in the barrel?
一桶油连桶重5.2千克，倒也一半油后，连桶还重2.7千克，桶里原来有油多少千克？
<gadget id="calculator">5.2 - 2.7</gadget>
<output>2.5</output>

<gadget id="calculator">2.5 * 2</gadget>
<output>5</output>

<result>5</result>