There is a batch of coal in a thermal power plant. On the first day, (1/7) of this batch of coal is used, the rest (1/6) is used on the second day, and the rest (1/5) is used on the third day. Use the rest (1/4) on the fourth day, and use the rest (1/3) on the fifth day. , Use the remaining (1/2) on the sixth day. , At this time there are 120 tons left. How many tons of coal was used on the first day?
某热电厂有一批煤炭，第一天用去这批煤炭的(1/7)，第二天用去剩下的(1/6)，第三天用去剩下的(1/5)，第四天用去剩下的(1/4)，第五天用去剩下的(1/3)．，第六天用去剩下的(1/2)．，这时还剩下120吨．问第一天用煤多少吨？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 - (1/3)</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<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">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">1 - (1/6)</gadget>
<output>5/6 = around 0.833333</output>

<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">1 - (1/7)</gadget>
<output>6/7 = around 0.857143</output>

<gadget id="calculator">120 / (1/2) / (2/3) / (3/4) / (4/5) / (5/6) / (6/7)</gadget>
<output>840</output>

<gadget id="calculator">840 * (1/7)</gadget>
<output>120</output>

<result>120</result>