To print a manuscript, A alone needs 50 minutes to complete it, and B alone needs 30 minutes to complete it. Now after A plays several copies alone, B continues to finish playing, a total of 42 points. Q: What percentage of the manuscript did A type?
打印一份稿件，甲单独需50分完成，乙单独打需30分完成．现在甲单独打若干份后，乙接着打完，共42分．问：甲打了稿件的几分之几？
<gadget id="calculator">1 / 50</gadget>
<output>1/50 = around 0.02</output>

<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">(1/30) * 42</gadget>
<output>7/5 = around 1.4</output>

<gadget id="calculator">(7/5) - 1</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(1/30) - (1/50)</gadget>
<output>1/75 = around 0.013333</output>

<gadget id="calculator">(2/5) / (1/75)</gadget>
<output>30</output>

<gadget id="calculator">(1/50) * 30</gadget>
<output>3/5 = around 0.6</output>

<result>3/5 = around 0.6</result>