# as a part of her statistics coursework, Dan records her bus journey times to school on a random samp

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as a part of her statistics coursework, Dan records her bus journey times to school on a random sample of 15 days. the times, in minutes are as follows
15.7 ,14.8 ,12.3, 18.6, 15.8, 13.4 ,14.7, 17.6 ,16.3
15.4 , 13.8 , 16.7 , 15.1 , 14.6, 12.6
A- use these data to estimate the mean and standard deviation of dan's bus journey time to school.
B- explain why dan did not somply record her bus journey times over a 3-week peroid.

20 September 2012

hi?

20 September 2012

is anyone here?

20 September 2012

A- mean = (sum of all data values)/ (number of different data value used, in this case 15). Standard deviation definition is a bit harder to write out here but you can find it by subtracting the value of the mean from every data value, squaring those 15 differences, summing them, dividing this answer by the number of data points again, and taking the square root of this number.

21 September 2012

For part B, ideally in statistics you should take a sample as random as possible, to eliminate if possible other variables. For example if there were road works happening along the route during the three-week period then this would likely lengthen the journey significantly. However on average journey times may really be shorter, and this is more likely to happen if you take 15 random days spread over a longer amount of time. So basically, it's to reduce the chance of some unknowns distorting the data.

21 September 2012

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