Question 1118905
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It's probably wrong of tutor @ikleyn to say the solution by the other tutor @theo is wrong.<br>
It seems LIKELY that the intent of the problem is to treat the time between 11 and 21 minutes as a continuous range of 10 minutes; however, it could be that the data points are expressed to the nearest minute, making the data values the 11 discrete values 11, 12, ..., 21, making the solution by tutor @theo valid.<br>
So the statement of the problem is unclear enough to allow different interpretations.<br>