Xiao Ming blows soap bubbles once every minute, exactly 100 soap bubbles are blown out each time. After the soap bubbles were blown out, half of them burst after one minute, and one-twentieth of them remained unbroken after two minutes, and all the soap bubbles burst after two and a half minutes. When Xiao Ming blows out 100 new soap bubbles for the 20th time, how many soap bubbles are not broken?
小明每分钟吹一次肥皂泡，每次恰好吹出100个．肥皂泡吹出之后，经过一分钟有一半破了，经过两分钟后还有二十分之一没有破，经过两分半钟肥皂泡全部破了．小明在第20次吹出100个新的肥皂泡的时候，没有破的肥皂泡共有多少个．
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">1 + (1/2) + (1/20)</gadget>
<output>31/20 = around 1.55</output>

<gadget id="calculator">100 * (31/20)</gadget>
<output>155</output>

<result>155</result>