A barrel of oil, 40 kg is used up, and the amount used is less than the rest (1/5). How many grams is there in the barrel of oil?
一桶油，用去40千克，用去的比剩下的少(1/5)，这桶油原来有多少克？
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">40 / (4/5)</gadget>
<output>50</output>

<gadget id="calculator">50 + 40</gadget>
<output>90</output>

<gadget id="calculator">90 * 1_000</gadget>
<output>90_000</output>

<result>90_000</result>