Master Li bought several apples at the price of 3 apples for 1 yuan, and sold these apples at the price of 2 apples for 1 yuan. The price sells the remaining apples. But in the end he not only earned 24 yuan, but also left 1 apple, so how many apples did he buy?
李师傅以1元钱3个苹果的价格买进苹果若干个，以1元钱2个苹果的价格将这些苹果卖出，卖出一半后，因为苹果降价只能以2元钱7个苹果的价格将剩下的苹果卖出．不过最后他不仅赚了24元钱，还剩下了1个苹果，那么他买了多少个苹果？
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">(1/3) - (2/7)</gadget>
<output>1/21 = around 0.047619</output>

<gadget id="calculator">(1/3) - (1/21)</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">24 + (2/7)</gadget>
<output>170/7 = around 24.285714</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) - (1/3) - (1/21)</gadget>
<output>5/42 = around 0.119048</output>

<gadget id="calculator">(170/7) / (5/42)</gadget>
<output>204</output>

<gadget id="calculator">204 * 2</gadget>
<output>408</output>

<result>408</result>