finding out AVERAGE broadband speed

I have collected over 120 observations of broadband internet speeds achieved through my service provider. The values range from, 5 kilobits per sec. to 256 kbps.

I need to determine the average speed achieved.

I am wondering whether 'arithmetic mean' or 'harmonic mean' is the appropriate measure for this purpose, and why?

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I think you should calculate the harmonic mean of the date. This is one of the very few occations in which AM can not provide a good answer. The reason is, the observations are just the rate of streaming of the data in one second, and the average speed is the ratio of the total quantity of data you obtained to the total time taken.