Solution to September 2000 brain teaser
In each case below the base unit is 100 observations:
If the car was black, the number of witnesses saying the car was black =									80.0000
If the car was green, the number of witnesses saying the car was black =							(40/90)*20=		8.8889
If the car was red, the number of witnesses saying the car was black =							(40/70)*20=		11.4286
If the car was white, the number of witnesses saying the car was black =							(40/80)*20=		10.0000
	Total number of replies saying the car was black						=		110.3175
Therefore the probability that the witness actually did see a black car =							(80/110.3175)=		72.52%