There are 4 white balls and several black balls of the same size and shape in an opaque pocket, only of different colors. Now draw out one ball each time, then put it back, stir well, and touch again. It is known that each time you touch The probability that a ball is white is (1/3), what is the number of black balls in the pocket
在一个不透明的口袋中装有大小、形状完全相同，只有颜色不同的4个白球和若干个黑球，现每次摸出一个球，然后放回，搅匀，再摸，已知每次摸出一个球是白球的可能性为(1/3)，则口袋中黑球的个数为多少
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">4 / (1/3)</gadget>
<output>12</output>

<gadget id="calculator">12 - 4</gadget>
<output>8</output>

<result>8</result>