The sum of the numbers A and B is 72, the number A is 20% less than the number B, what is the number B?
甲、乙两数的和是72，甲数比乙数少20%，乙数是多少．
<gadget id="calculator">20 / 100</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">(4/5) + 1</gadget>
<output>9/5 = around 1.8</output>

<gadget id="calculator">72 / (9/5)</gadget>
<output>40</output>

<result>40</result>