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# Guesstimate Methods and Examples

GUESTIMATE methods are a combination of mathematics, statistics and common sense of getting meaningful results for decision making.
The most famous approach was suggested by Enrico Fermi. Mr. Fermi was convinced that an error of order of magnitude (up to ten times) can be accepted for certain problems.
There are many useful results can be obtained by using probability estimation.
Expected values are largely used in economics, business, finance, and opportunity choice.
Old fashion rule of thumb is a widely used approach among non-mathematicians.
Certain results can be obtained if we consider either limits or average values of variables.

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### Guesstimate Methods and Examples

1. 1. Introduction to Guesstimate © 2016 Aplusclick
2. 2. Guesstimate Things are not certain (or known). To receive meaningful results. An estimate based on a mixture of guesswork and calculation. © 2016 Aplusclick
3. 3. Methods & Objective “Everything should be made as simple as possible, but not simpler.” – Albert Einstein “The purpose of computing is insight, not numbers.” – Richard Hamming Albert Einstein (image source: Wikipedia) Richard Hamming (image source: Wikipedia)© 2016 Aplusclick
4. 4. Guesstimate Techniques Fermi Problem Probability Expected Value Rule of Thumb Limits, Average, and Big Numbers . . . . © 2016 Aplusclick
5. 5. Fermi Problem Making justified guesses about variances, lower and upper bounds. "How many piano tuners are there in Chicago?” Steps: 1. There are approximately 9,000,000 people living in Chicago. 2. On average, there are two persons in each household in Chicago. 3. Roughly one household in twenty has a piano that is tuned regularly. . . . Enrico Fermi (image source: Wikipedia) © 2016 Aplusclick
6. 6. Example: Reading How much time does it take to read all books on “Data Science” in English? 1200 books are available on Amazon. I estimate my capacity as 50 pages per day. I assume that there are 250 pages on average. So, it takes 1200 • 250 / 50 = 6000 working days or about 30 years. © 2016 Aplusclick
7. 7. Probability Estimation A dealer has 40 brand new cars to sell. He paid \$40,000 per car. He hopes that half of the new cars will sell at the original price he sets, 40% of the remainder will sell later when their price is reduced by 10%, and the rest of the cars will sell in a clearance sale at only 80% of the original price. In order to make an expected profit, the total sales revenue must be \$6,000 on average for each car. What original price should the dealer set? © 2016 Aplusclick
8. 8. Expected Values I have ten thousand dollars in the Mad Money's bank account. The interest rate is 100% every year. My guess: the probability of the bankruptcy of the bank is 50% every year. What is the expected amount of my money after three years? © 2016 Aplusclick
9. 9. Rule of Thumb An estimation that is not intended to be strictly accurate. Example: Estimate the number of words in English language and compare it with other languages. © 2016 Aplusclick
10. 10. Limits and Average An estimation that is not intended to be strictly accurate. © 2016 Aplusclick
11. 11. Time of getting it useful Accuracy 102 101 Time of problem solving © 2016 Aplusclick
12. 12. Example: Error Detection John detected two errors and Mary three errors in a code. There is one error in common. How many errors are still undetected? «Testing proves the presence of bugs but not their absence» - Woody Williams © 2016 Aplusclick
13. 13. Example: Error Detection John detected two errors and Mary three errors in a code. There is one error in common. How many errors are still undetected?N = number of errors; 2/N = John’s rate; 3/N = Mary’s rate; (2/N) × (3/N) = (1/N) N = 6 6 – 2 – 3 + 1 = 2 errors are undetected © 2016 Aplusclick
14. 14. Examples -What are the chances to meet your true love in Lausanne? -How many tennis balls can fit in a school bus? -What is the probability that two 10-minute phone calls do not intersect in 1-hour period? -How many "yes or no" questions are needed to guess any 5-digit code? Answers: www.aplusclick.com/guesstimate.htm © 2016 Aplusclick
15. 15. Generalization Keep searching hypothesis, data until reaching meaningful results. Practice makes perfect. © 2016 Aplusclick
16. 16. Literature L.Weinstein, J.A.Adams Guesstimation: Solving the World’s Problems on the Back of a Cocktail Napkin, 2008, Princeton University Press. www.aplusclick.com/guesstimate.htm Answers © 2016 Aplusclick