A commodity is sold at a profit of 40%. After half of the product is sold, the other half is sold at a 50% discount. What is the profit margin?
一件商品以40%的利润出售，售出一半后，另一半打5折出售，那么利润率是多少．
<gadget id="calculator">0.35 - 1</gadget>
<output>-0.65</output>

<gadget id="calculator">0.7 + (-0.65)</gadget>
<output>0.05</output>

<gadget id="calculator">0.05 / 1</gadget>
<output>0.05</output>

<result>0.05</result>