# [HW 2.2b] From the world of sensor networking.

Here are two lists of sensors that were deployed at various points in times.  Each list contains both a MAC ID and a deployment date.

You need to compare these lists and determine:

1. How many of the MAC IDs on Our List are not on Their List?
2. How many of the MAC IDs on Their List are not on Our List?
3. How many of the MAC IDs on Our List are also on Their List?
4. As a control total, what is the sum of the dates that are on Their List but not Our List?
HW 2-2.Two lists

How does one complete step 4 of this assignment? We tried using =MATCH & =SUMIF, but none of them work. Any help would be appreciated!

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1. Step four was to sum the dates. =SUM should work.

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1. I got another question about #4:

For “4. As a control total, what is the sum of the dates that are on Their List but not Our List” my group is confused on how to do this. We used COUNTIF on the previous questions however when we attempted to do this with dates we get very large numbers that can’t be accurate. Therefore we aren’t sure how to go about this since it is not dealing with dates rather than integers. Not sure if you could break it down a little more for us so we understand it better, but any guidance would be appreciated.

The basic idea is that since dates are stored as numbers, they can be added. For example, today is 1/13/15 and tomorrow is 1/14/15. In excel, these dates are stored as 42,017 and 42,018. So if you add 1/13/15 and 1/14/15, you will get 84,035.

So, one way to check the accuracy of whether you identified all of the MAC IDs that were on our list but not their list is to have you add up the install dates of all of those sensors. You’ll get a large number that is meaningless, except for its usefulness as a control total.

Does that make more sense?

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