The measure ratio of the apex angle to the base angle of an isosceles triangle is 1:4. What is the measure of the base angle of an isosceles triangle?
一个等腰三角形的顶角和一个底角的度数比是1：4，它的一个底角是多少度．
<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>