Master Zhang bought some fruits for 1 yuan and 3 apples, and sold them for 2 yuan and 5 apples. Then how many apples does he have to sell to make a profit of 10 yuan.
张师傅1元钱3个苹果买进一些水果，又以2元钱5个苹果卖出．那么他要卖出多少个苹果才能赚得10元钱的利润．
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">(2/5) - (1/3)</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">10 / (1/15)</gadget>
<output>150</output>

<result>150</result>