An oil barrel, after filling (2/5) barrels of peanut oil, the total weight of the barrel is 3.5 kg, and the total weight of the barrel is 6.5 kg. How much does this barrel of oil weigh?
一个油桶，装进(2/5)桶花生油后，连桶共重3.5千克，把桶装满连桶共重6.5千克，这桶油重多少千克？
<gadget id="calculator">6.5 - 3.5</gadget>
<output>3</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">3 / (3/5)</gadget>
<output>5</output>

<result>5</result>