[tex]average = \frac{sum \: \: of \: \:all \: \: obeservations}{no. \: \: of \: observaions} [/tex]
[tex] = \frac{1205 + 1450 + 1530 + 1655 + 1610 + 1710}{6} [/tex]
[tex] = \frac{9160}{6} [/tex]
[tex] = 1526.66[/tex]
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1526.66 is the average of his sales for this period.