A barrel of oil weighs 100 kilograms. The barrel of oil is used (1/10) and the barrel of oil is bought later (1/10). How many kilograms of oil is in the barrel at this time?
一桶油重100千克，用去这桶油的(1/10)，以后又买来这桶油的(1/10)，这时桶里有油多少千克．
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">1 - (1/10)</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">100 * (9/10)</gadget>
<output>90</output>

<gadget id="calculator">100 * (9/10) * (1/10)</gadget>
<output>9</output>

<gadget id="calculator">90 + 9</gadget>
<output>99</output>

<result>99</result>