A project can be completed by A alone in 15 days and B by himself in 10 days. Now A and B will work together for 3 days, and then B will continue to do it. What fraction of the project does B need to do to complete the task?
一项工程，甲独做15天完成，乙独做10天完成．现在先甲、乙合做3天后再由乙接着做，乙需要再做这项工程的几分之几就完成任务？
<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/15) + (1/10)</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">(1/6) * 3</gadget>
<output>1/2 = around 0.5</output>

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

<result>1/2 = around 0.5</result>