My mother bought a barrel of peanut oil, and after using it for two weeks, there was still 1.8 kilograms left. It is known that 30% of the total was used in the first week and 1.7 kg in the second week. How much is this barrel of oil?
妈妈买了一桶花生油，用了两周后还剩1.8千克．已知第一周用了总数的30%，第二周用了1.7千克．这桶油一共有多重？
<gadget id="calculator">1.8 + 1.7</gadget>
<output>3.5</output>

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

<gadget id="calculator">1 - (3/10)</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">3.5 / (7/10)</gadget>
<output>5</output>

<result>5</result>