Posted by Peder Enhorning

March 19, 2013

11:20 am

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Tableau and Counting Money

We just returned from a road show to promote the new Tableau version 8. As a sponsor, we came equipped with a barrel full of single dollar bills. The offer was that whoever guessed closest to the actual amount of bills could keep the cash.

Keeping track of money is one of the most fundamental skills we have today. We were taught how to count with building blocks as toddlers and how to quickly split the bill when going on a double-date.

Cash-Barrel-e1363711726925

As (brilliantly) trained analysts we are expected to quickly calculate totals and estimate values. We do it every day and are pros at it. We take terabytes of data with millions of rows of complex numbers, and to help others understand it, we create beautiful Tableau dashboards to share with them. We already understand the data (because we are number experts!), and now it’s easy to share it so others do as well.

So estimating a barrel full of single dollar bills should be easy, right? But according to the guesses we had, apparently it’s not. Guesstimates ranged from $44 to $888.

Strategies for Success

There are a few strategies you could have used in calculating the number of bills in our barrel.

1) Guess. It’s just a game.

2) Count them. Don’t count each dollar, of course, but you could count the number of bills in a two or three inch vertical section and multiply that number times the number of similar sections in the container. This could yield a very good estimate.

3) Equate them. This strategy is best if you are “guessing” the number of bills in a known volume. In fact, it’s almost fool-proof in that situation.

The measurement of a dollar bill is 2.5 inches X 6 inches. The volume of one crumpled bill can be thought of as a cubic space taking up 2 inches X 1 inches (slightly thicker because it’s crumpled) X 5 inches (slightly shorter because it’s crumpled) which is 10 cubic inches per dollar bill.

The formula for calculating the volume of a cylinder is V=πr2h. The barrel we used measured 24 inches in height with a radius of 6 inches. And it was filled to about 18 inches. The Volume, therefore, is V= 3.14159 X  62 X 18 = 2035 cubic inches.

The calculated answer, therefore, is 203 since that’s how many 10 cubic inch bills it would take to fill that space. The right answer was in fact 201.

Who’s the smartest?

Who do you think correctly guessed calculated the dollar amount in our Cash Barrel!? Well, it wasn’t a highly paid data specialist attending the roadshow to see the latest features of Tableau. Instead, it was a woman from the catering staff at the Hyatt in Jersey City! Let’s call her Carmen (not her real name since I’m not sure the hotel would have allowed her to participate). Carmen nonchalantly said she was great with numbers and quickly and correctly answered the challenge! We sent her $201 which she enthusiastically accepted!

Thanks to everyone for participating. Check out the viz we created.
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