What is the area of a rectangle with a perimeter of 30 cm and a ratio of length to width of 2:1?
一个长方形的周长30厘米，长和宽的比是2：1，它的面积是多少．
<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<gadget id="calculator">2 + 1</gadget>
<output>3</output>

<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">15 * (2/3)</gadget>
<output>10</output>

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

<gadget id="calculator">15 * (1/3)</gadget>
<output>5</output>

<gadget id="calculator">10 * 5</gadget>
<output>50</output>

<result>50</result>