Question 1175319
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The given uncertainty interval is 20 seconds long (20 = 10 + 10 seconds).


The base uncertainty interval is  4 minutes long (4 = 2 + 2 minutes), or 4*60 = 240 seconds.


The probability under the problem's question is the ratio  {{{20/240}}} = {{{1/12}}}.     <U>ANSWER</U>
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Solved.