The three brothers want to jointly buy a bicycle with a price of 900 yuan. The eldest child pays twice as much as the second child, and the third child pays the average of the first and second child. So how much did the second child pay?
兄弟三人要合买一辆价格为900元的自行车．老大付的钱是老二所付钱数的两倍，老三付的钱是老大和老二的平均值．那么老二付了多少元钱．
<gadget id="calculator">1 + 2</gadget>
<output>3</output>

<gadget id="calculator">3 / 2</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">1 + 2 + (3/2)</gadget>
<output>9/2 = around 4.5</output>

<gadget id="calculator">900 / (9/2)</gadget>
<output>200</output>

<result>200</result>