A section of the road is 400 meters long. A can complete it in 10 days alone, and B can complete it in 4 days (1/2). Now A and B will repair it together for 3 days. How many days will A need to complete the whole project?
一段路长400米，甲独修10天完成，乙独修4天可完成(1/2)，现先由甲乙合修3天后，余下的甲还要修多少天才能完成全工程？
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

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

<gadget id="calculator">(1/2) / 4</gadget>
<output>1/8 = around 0.125</output>

<gadget id="calculator">(1/10) + (1/8)</gadget>
<output>9/40 = around 0.225</output>

<gadget id="calculator">(9/40) * 3</gadget>
<output>27/40 = around 0.675</output>

<gadget id="calculator">1 - (27/40)</gadget>
<output>13/40 = around 0.325</output>

<gadget id="calculator">(13/40) / (1/10)</gadget>
<output>13/4 = around 3.25</output>

<result>13/4 = around 3.25</result>