The ratio of the radii of the three concentric circles is 3:4:5. If the area of the large circle is 100 square centimeters, what is the area of the ring formed by the middle circle and the small circle?
三个同心圆的半径之比是3：4：5，如果大圆的面积是100平方厘米，那么中圆与小圆构成的圆环面积是多少平方厘米？
<gadget id="calculator">16 / 25</gadget>
<output>16/25 = around 0.64</output>

<gadget id="calculator">100 * (16/25)</gadget>
<output>64</output>

<gadget id="calculator">9 / 25</gadget>
<output>9/25 = around 0.36</output>

<gadget id="calculator">100 * (9/25)</gadget>
<output>36</output>

<gadget id="calculator">64 - 36</gadget>
<output>28</output>

<result>28</result>