[tempfile]

For small probabilities it works :)

1-(1-p1)(1-p2) = p1+p2-p1p2

and a similar formula holds for more terms. so neglecting terms of order p^2 gives the form in the article

[sebastiennight]

For probabilities (much) smaller than 10%, sure.

But adding 10%, 20%, and 35%, is already a pretty bad start. The error rate becomes huge. (in the article example, the 10% estimate of chances of being on time is ~3.5 smaller than the actual 35% correct result).

Being wrong by half an order of magnitude, is being quite wrong :)

[tempfile]

I'm not disagreeing with you!