Kindergarten middle class and senior class have the same number of balls. After the number of senior class increases, the middle class gives a ball to the senior class. In order to engage in activities in the kindergarten, the senior class and the middle class each take out a ball. Now the number of balls in the senior class is the middle class. 2 times, how many balls are there in the middle class and the big class?
幼儿园中班、大班的皮球数一样多，大班人数增加后，中班给了大班一个皮球，幼儿园为搞活动，大班、中班又各拿出一个球，则现在大班的皮球数是中班的2倍，原来中班、大班一共有多少个皮球．
<gadget id="calculator">1 + 1</gadget>
<output>2</output>

<gadget id="calculator">2 - 1</gadget>
<output>1</output>

<gadget id="calculator">2 * 1 * 2 * 1</gadget>
<output>4</output>

<gadget id="calculator">2 * 1</gadget>
<output>2</output>

<gadget id="calculator">4 + 2 + 1 + 1</gadget>
<output>8</output>

<result>8</result>