There are 75 white rabbits, and the number of black rabbits is 2/5 of that of white rabbits. How many black rabbits are there?
白兔有75只，黑兔的只数是白兔的(2/5)，黑兔有多少只？
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">75 * (2/5)</gadget>
<output>30</output>

<result>30</result>