A pocket contains 5 white balls, 7 black balls, and 4 red balls of the same shape and size. What is the probability that 3 balls are drawn from the pocket and there are exactly 2 black balls and 1 red ball?
一个口袋里装有形状大小均相同的5个白球、7个黑球和4个红球，从中取出3个球，恰好两个黑球和一个红球的可能性是百分之几？
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<result>1/10 = around 0.1</result>