Anne, Edward, and Isaac are the three editors of the Perplexus Weekly newspaper. This week, Anne spotted 300 errors, Edward spotted 100 errors, and Isaac spotted 200 errors. Altogether, they spotted 404 errors. Assuming that each error is equally easy to spot, about how many errors did they miss?

Let x be the number of errors, assume 100/x, 200/x, and 300/x are good estimates of individual error spotting probabilities and assume that 404/x is a good estimate of the probability of an error being spotted by at least one of the three.

Probability of being spotted by at least one of the three is equal to probability of being spotted by Edward plus the probability of being spotted by Isaac and not Edward plus the probability of being spotted by Anne and not Edward nor Isaac.
404/x = (100/x)+(200/x)((x-100)/x)+(300/x)((x-100)/x)((x-200)/x)
This has two solutions, with only one beingan integer; x=500.

Now, what if the probability of any person spotting an error is equal, what would be a "best" estimate then?

Posted by owl on 2006-02-15 07:33:27