There are 90 people in Class A and Class B. The number of people in Class A is (4/5) the number of people in Class B. How many people are there in Class B?
甲乙两班共有90人，甲班人数是乙班人数的(4/5)，乙班有多少人．
<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">90 / (9/5)</gadget>
<output>50</output>

<result>50</result>