In an isosceles triangle, the degree ratio of its top angle to a base angle is 1:4, what is the top angle of this isosceles triangle?
一个等腰三角形中，它的顶角与一个底角的度数比是1：4，这个等腰三角形的顶角是多少度？
<gadget id="calculator">1 + 4 + 4</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>