There is a bag of rice, 40% of which was eaten in the first week, and 12 kilograms in the second week, and there is still 30% left. How much does this bag of rice weigh?
有一袋大米，第一周吃了40%，第二周吃了12千克，还剩30%，这袋大米原来有多重？
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 - (2/5) - (3/10)</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">12 / (3/10)</gadget>
<output>40</output>

<result>40</result>