There are 84 oranges in a basket, take out the total (1/21) for the first time, take out the remaining (1/20) for the second time, and take out the remaining (1/19) for the third time... Take out the remaining (1/2) of the 19th time 20 times, how many oranges are left in the basket at this time?
一筐橘子有84个，第一次取出总数的(1/21)，第二次取出第一次余下的(1/20)，第三次取出第二次余下的(1/19)…第20次取出第19次余下的(1/2)，这时筐中还剩下多少个橘子？
<gadget id="calculator">1 / 21</gadget>
<output>1/21 = around 0.047619</output>

<gadget id="calculator">84 * (1/21)</gadget>
<output>4</output>

<gadget id="calculator">84 - 4</gadget>
<output>80</output>

<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">80 * (1/20)</gadget>
<output>4</output>

<gadget id="calculator">80 - 4</gadget>
<output>76</output>

<gadget id="calculator">1 / 19</gadget>
<output>1/19 = around 0.052632</output>

<gadget id="calculator">20 * 76 * (1/19)</gadget>
<output>80</output>

<gadget id="calculator">84 - 80</gadget>
<output>4</output>

<result>4</result>