(4/5) of the number of people in class A is equivalent to the number of people in class B, and the total number of people in the two classes is 81. How many people are in Class A?
甲班人数的(4/5)相当于乙班人数，两个班总人数是81人．甲班多少人．
<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 + (4/5)</gadget>
<output>9/5 = around 1.8</output>

<gadget id="calculator">81 / (9/5)</gadget>
<output>45</output>

<result>45</result>