Your SlideShare is downloading. ×
!    !    !                                                                                               !               ...
!                !!!!!!!!!!!!!!                                                        !                                  ...
!           !  &%&!0/!9%&)!&--0F41&.%)!&*!*A:&%#!39%!&5*"%!7&5!;%!%/45%)!;B!41-0@456!.9%!%&*05456+!.9&.!.9%!  9&4!)%5*4.B!...
!            !  ;%&:.4/:88B!;%&>*! )0"5! .9%!-0;8%1! &*! &! 7088%7.405! 0/! @&40:*! -0/4.&;484.B!10)%8*!&5)!.%&79%*!.94*! ...
Upcoming SlideShare
Loading in...5
×

How many hairs do you have on your head?

1,149

Published on

This article uses the analogy of counting hairs on your head to illustrate scientific approximations and its usefulness in software testing. The article was published in the August 2001 issue of Tea Time with Testers, an ezine.

Published in: Education
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total Views
1,149
On Slideshare
0
From Embeds
0
Number of Embeds
2
Actions
Shares
0
Downloads
5
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

Transcript of "How many hairs do you have on your head?"

  1. 1. ! ! ! ! ! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !! ! ! ! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ! ! ! !! ! ! !! ! ! !
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h!0.9%"4*%!4 .9&.!4.!.:5*!0:.!.0!;%!70%7.#! ! C.!4*!41-0.&5.!.0!:5)%*.&5)!.9&.!&5!%F&7.!@&8:%!1&B!50.!;%!%A:4%)h!&.9%! 4.!4*!.9%!%&*05456!.9&.! &880"*! :*! .0! 701%! :-! "4.9! &! @&8:%+! &5)! 705*.&5.8B! 41-0@456! .9%! %&*05456! .0! ;%..%! .9%! @&8:%#! 39%! *41-8%*.! "&B! ! .0! 701-:.%! .94*! ;B! 1:8.4-8B456! .9%! )%5*4.B! 0/! 9&4! &5)! !!!"""#!"#!$%"&$!!"(!")(*+,%!!!!!!!!!!!!!!!!!!!!!!!!!---------------------------------------------------------------!"#"$%&&()).*.! !
  3. 3. ! ! &%&!0/!9%&)!&--0F41&.%)!&*!*A:&%#!39%!&5*"%!7&5!;%!%/45%)!;B!41-0@456!.9%!%&*05456+!.9&.!.9%! 9&4!)%5*4.B!@&4%*!&70**!.9%!9%&)!&5)!.9&.!"%!1&B!5%%)!.0!705*4)%!.9%!7:@&.:%!/&7.0!0/!9%&)+!9&4! *9%)!&.%!%.7#! ! 20!"9&.!&%!"%!)0456Y!(&.9%!.9&5!<:*.!6:%**!*01%90"+!"%!9&@%! .4%)!.0!705*.:7.!&!*41-8%!/01:8&! .9&.!4*!705.45:&88B!%/45%)!.0!;%..%!.9%!0:.701%#!K0.%!.9&.!"9&.!"%!9&@%!)05%!4*!.9%!&6%!08)!-0;8%1! *08@456!.%7954A:% ! ! ! ! ! ! ! ! ! ! ! ! ! 39%!&7.!0/!&--0F41&.405!4*!@%B!5&.:&8h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r*7%5&40*+! r7B78%*+! .41%*! 45@08@%)! 45! :5)%*.&5)456+! )%*465+! &:.01&.405+! %F%7:.405+!10)%!0/!%F%7:.405+!@08&.484.B!0/!&!/%&.:%+!.B-%*!0/!.%*.*!%.7#! ! C! 9&@%! 0;*%@%)! .9&.! "9%5! -%0-8%! )%*465! 80&)+! *.%**+! -%/01&57%+! *7&8&;484.B! &5)! @08:1%! .%*.*+! .9%! .%*.!)&.&!@&8:%*!:*%)!/0!80&)!-0/48%+!*4?%!0/!)&.&!&%!*%%14568B!600)!6:%**%*#!274%5.4/47!&--0F41&.405! .0! %*.41&.%! .9%! 80&)! 70:8)! ;%! ;&*%)! 05! .9%*%! @&4&;8%*I! .B-%*! 0/! %5)! :*%*+! r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
  4. 4. ! ! ;%&:.4/:88B!;%&>*! )0"5! .9%!-0;8%1! &*! &! 7088%7.405! 0/! @&40:*! -0/4.&;484.B!10)%8*!&5)!.%&79%*!.94*! .0! 94*!-0.k6k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i.94:#! ! ! ! ! &&&&&&&&&&&&&&&&&&&&&&&&& R9G#34SL=& ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ?!<@,.!4*!.9%!_0:5)%!m!JNS!0/!23,G!20/."&%! ! V4@&.%!=414.%)#! - ! ! V&**405&.%!&;0:.!%F7%88%57%+!94*!14**405!4*!.0! ! ! ! ! ! P%!7&5!;%!%&79%)!&.!#@,c@&#A@.7&U#*-]6.) . -!!!"""#!"#!$%"&$!!"(!")(*+,%!!!!!!!!!!!!!!!!!!!!!!!!!---------------------------------------------------------------!"#"$%&&()).*0! !

×