It takes 35 days for a project to be completed by B alone. If A works on the first day and B works on the second day, doing this alternately, the exact number of days will be completed. If B does the first day and A does the second day alternately, it just takes half a day longer to complete the project than the last time. How many days does it take for A to complete this project alone?
一项工程由乙单独完成需要35天，如果甲做第一天，乙做第二天，这样交替做，恰好整天天数完成．如果乙做第一天，甲做第二天，这样交替做，恰好比上次轮流的方法多用半天完成，求甲单独完成这项工程需要多少天？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">35 * (1/2)</gadget>
<output>35/2 = around 17.5</output>

<result>35/2 = around 17.5</result>