The average of the two numbers of A and B is 72, and the number of A is 20% less than the number of B. What is the number B.
甲、乙两数的平均数是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">2 / (9/5)</gadget>
<output>10/9 = around 1.111111</output>

<gadget id="calculator">72 * (10/9)</gadget>
<output>80</output>

<result>80</result>