Illusions Virus - Page 1
Please note - this is just a puzzle. The ILLUSIONS virus does not really exist!
Government scientists have established that a very serious virus, the ILLUSIONS virus, has infected the population. At present it shows no symptoms, and it is not known how it spreads from person to person. The government scientists, using very sophisticated equipment, have established for certain that 1 person in a thousand is infected.
Your local chemist is offering a do-it-yourself testing kit, which is simple and cheap. However it is only 95% accurate, i.e. if you have the virus there is a 95% chance it will predict this correctly, and a 5% chance it will be wrong, and tell you you do not have the virus. Likewise, if you do not have the virus, there is a 95% chance it will tell you that you are OK, and a 5% chance it will tell you that you have the virus.
You buy a kit, and it tests positive, i.e. it is telling you that you have the virus.
What is the actual probability that you have the ILLUSIONS virus?
Photo courtesy of kreg.steppe on flickr.