20% of a number is 50, what is 30% of this number?
一个数的20%是50，这个数的三成是多少．
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">50 / (1/5)</gadget>
<output>250</output>

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

<gadget id="calculator">250 * (3/10)</gadget>
<output>75</output>

<result>75</result>