Thank you for commenting and I am glad that the article was helpful.

For calculating the value, P(test positive):

P(test positive) = P(positive|disease)*P(disease) + P(positive|no disease)P(no disease) = (0.99*0.001) + (0.01)*(0.999) = 0.01098

I hope this answers your question :)

Let me know if you have further questions on this or something is not clear..