The perimeter of a rectangle is 30 cm. If the ratio of length to width is 2:1, what is the width of the rectangle in centimeters?
一个长方形周长为30cm，若长与宽的比为2：1，则长方形的宽为多少厘米．
<gadget id="calculator">2 + 2 + 1 + 1</gadget>
<output>6</output>

<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">30 * (1/6)</gadget>
<output>5</output>

<result>5</result>