A box contains several black, white, and red beads of different colors. Among them, the number of red beads is 1/7 of that of white beads, and the number of black beads is 50% of that of red beads. If any bead is drawn from the box, what is the probability of drawing a black bead?
在一个盒子里装着只有颜色不同的若干黑、白、红三种颜色的珠子，其中红色珠子的颗数是白色的(1/7)，黑色珠子的颗数是红色珠子的50%．如果从盒子中任意摸出一颗珠子，摸出黑色珠子的可能性是多少．
<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">50 / 100</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/7) * (1/2)</gadget>
<output>1/14 = around 0.071429</output>

<gadget id="calculator">1 + (1/7) + (1/14)</gadget>
<output>17/14 = around 1.214286</output>

<gadget id="calculator">(1/14) / (17/14)</gadget>
<output>1/17 = around 0.058824</output>

<result>1/17 = around 0.058824</result>