The school breeding group raises 15 white rabbits, the number of black rabbits is 2/3 of that of white rabbits, and the ratio of the number of gray rabbits is 2:7. How many gray rabbits do you have?
学校饲养小组养白兔15只，黑兔的只数是白兔的(2/3)，与灰兔只数的比是2：7．养灰兔多少只？
<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">7 / 2</gadget>
<output>7/2 = around 3.5</output>

<gadget id="calculator">15 * (2/3) * (7/2)</gadget>
<output>35</output>

<result>35</result>