The auntie in the kindergarten gave a box of biscuits to the children in the big and small classes of the kindergarten. On average, each child received 12 yuan. If it was only given to the children in the small class, each person could get 20 yuan. How many pieces can a person get.
幼儿园的阿姨把一箱饼干发给一个幼儿园大、小班的小朋友，平均每个小朋友发到12块，若只给小班的小朋友，每人可分到20块，若只分给大班的小朋友，每人可以分到多少块．
<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

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

<gadget id="calculator">(1/12) - (1/20)</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">1 / (1/30)</gadget>
<output>30</output>

<result>30</result>