The ratio of a base angle to an apex angle of an isosceles triangle is 1:4, what is the apex angle of this isosceles triangle?
一个等腰三角形的一个底角与顶角度数的比是1：4，这个等腰三角形的顶角是多少度．
<gadget id="calculator">1 + 1 + 4</gadget>
<output>6</output>

<gadget id="calculator">4 / 6</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">180 * (2/3)</gadget>
<output>120</output>

<result>120</result>