1.
Introduction to Guesstimate
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2.
Guesstimate
Things are not certain (or known).
To receive meaningful results.
An estimate based on a mixture of guesswork and
calculation.
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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.
Guesstimate Techniques
Fermi Problem
Probability
Expected Value
Rule of Thumb
Limits, Average, and Big Numbers
. . . .
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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)
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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.
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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?
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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?
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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.
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10.
Limits and Average
An estimation that is not intended
to be strictly accurate.
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11.
Time of getting it useful
Accuracy
102
101
Time of problem solving
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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
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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
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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
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15.
Generalization
Keep searching hypothesis,
data until reaching meaningful
results.
Practice makes perfect.
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16.
Literature
L.Weinstein, J.A.Adams Guesstimation: Solving the
World’s Problems on the Back of a Cocktail Napkin,
2008, Princeton University Press.
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Answers
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