The store brings in 250 red balloons and some yellow balloons. After selling 50 red balloons, the remaining number is twice as many as the yellow balloons. How many yellow balloons are brought in to the store?
商店运进250只红气球和一些黄气球，红气球卖出50只以后，剩下的只数是黄气球的2倍，商店运进黄气球多少只？
<gadget id="calculator">250 - 50</gadget>
<output>200</output>

<gadget id="calculator">200 / 2</gadget>
<output>100</output>

<result>100</result>