The ratio of the three interior angles of a triangle is 1:3:5, what is the smallest angle in this triangle?
三角形的三个内角之比为1：3：5，那么这个三角形中最小的角是多少．
<gadget id="calculator">1 + 3 + 5</gadget>
<output>9</output>

<gadget id="calculator">1 / 9</gadget>
<output>1/9 = around 0.111111</output>

<gadget id="calculator">180 * (1/9)</gadget>
<output>20</output>

<result>20</result>