The ratio of the number of boys and girls in class 51 is 1:4. If you choose a boy, what is the probability of being selected?
五1班男女生人数之比是1：4，任选一名男生，选中的可能性是多少．
<gadget id="calculator">1 + 4</gadget>
<output>5</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<result>1/5 = around 0.2</result>