1. Using Groups to analyze Data: Parallel Processing
Money from Horses
Prepared by J. Scott Armstrong (details on him at jscottarmstrong.com).
Please inform Scott about errors and also make suggestions (armstrong@wharton.upenn.edu)
Scott has taken these slides from adprin.com, a site that he founded. That site contains interactive versions of these
slides, along with linked references, videos, and webcasts, all in PPT and PPTX format that you can download.

2. The Horse Business
“A man bought a horse named Harry for $60 and sold
him for $70. Missing Harry, he bought him back for
$80. Finally, he sold Harry for $90. How much money
did he make in the horse business?”
Solve individually (usually half the
people get this correct). Spend 2 minutes.
Adapted from AdPrin.com 2

3. The Animal Business
“A man bought a horse named Harry for $60
and sold him for $70. He also bought a pig
named Pete for $80 and sold him for $90. How
much money did he make in the animal
business?”
Did your answer differ from that in the horse
business? Why?

4. The answer for the horse business is $20. Some people say
$10, and $30 comes up also. In a group someone nearly
always has the right answer. If people solve this individually
and then and discuss it, the group solutions are correct for the
vast majority of groups.
Now to the “animal business” question. Mathematically, it is
the same problem, but nearly everyone gets the correct
answer. This is because the horse question leads them astray.
Advice for doing analyses with groups:
1. Use parallel processing (each person solves the same
problem independently), then check with each other and
discuss it.
2. State the problem in different ways and solve those
problems.
Adapted from AdPrin.com 4

5. Based on this exercise, write a small application step for
yourself, and set a deadline, preferably within one week. If you
are working with someone else, share your application plan and
the results of your application.
• For example, ask someone to check any important analyses in
a report that you are currently working on.
Adapted from AdPrin.com