I'm sorry Hog but that is absolutely not true.

The chances of that test (ie the red one) being CB is 1 in 3

The chances of it being rider #2 is 1 in 3

The chances of it being rider #3 is 1 in 3

In fact the chances of that test being any one of the 3 tested riders is 1 in 3 - that's because 3 samples were taken from 3 different people (and lets assume 3 people were tested - to take 3 samples from 2 people would be odd).

As I'm sure you know the sum of all probabilities has to add up to 100% (or 3 in 3 in this case).

So if the chances of the sample belonging to CB is 1/3, the chance of it belonging to a rider other than CB is 2/3.

The

**results **of the other tests are irrelevant, otherwise you are confusing the actual results with the who the test belongs to.

Now, where I do agree is that the chances that CB returned a +ve (if only visual) test are AT LEAST 33.3333%. If we knew the outcome of the other 2 we could be more precise (especially if all 3 were +ve

)