sporting goods store buys a batch of small soccer balls at a price of 40 yuan each and sells them at a price of 50 yuan each. When 90% of these footballs were sold, not only the cost was recovered, but also a profit of 800 yuan was made. How many small footballs are there in total?
体育用品商店以每个40元的价格购进一批小足球，以每个50元的价格卖出．当卖掉这批足球的90%时，不仅收回了成本，还获利800元．这批小足球一共多少个？
<gadget id="calculator">90 / 100</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">50 * (9/10)</gadget>
<output>45</output>

<gadget id="calculator">45 - 40</gadget>
<output>5</output>

<gadget id="calculator">800 / 5</gadget>
<output>160</output>

<result>160</result>