The store shipped in a batch of apples, sold them in the morning (2/7), and sold them in the afternoon (1/7), what fraction is left?
商店运进一批苹果，上午卖出了(2/7)，下午卖出了(1/7)，还剩几分之几？
<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">(2/7) + (1/7)</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">1 - (3/7)</gadget>
<output>4/7 = around 0.571429</output>

<result>4/7 = around 0.571429</result>