A swarm of bees, among which (1/5) landed on rhododendrons, (1/3) landed on roses, among the remaining 21 bees, except for 7 flying around among the flowers, the rest all landed. On the Chinese rose. How many bees are there in this colony?
一群蜜蜂，其中(1/5)落在杜鹃花上，(1/3)落在玫瑰花上，剩下的21只蜜蜂中，除了有7只在花丛间飞来飞去，其余的都落在了月季花上．这群蜜蜂一共有多少只？
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 - (1/5) - (1/3)</gadget>
<output>7/15 = around 0.466667</output>

<gadget id="calculator">21 / (7/15)</gadget>
<output>45</output>

<result>45</result>