Put two kinds of balls, red balls and white balls, in a box, the total number does not exceed 20, so that the probability of drawing a white ball is (1/5), how many different ways are there in total?
往一个箱子里放入红球和白球两种球，总个数不超过20个，使摸出白球的可能性是(1/5)，一共有多少种不同放法．
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/5) / 5</gadget>
<output>1/25 = around 0.04</output>

<gadget id="calculator">5 * (1/25)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">20 * (1/5)</gadget>
<output>4</output>

<result>4</result>