Every day this week, my bus, the C2, has sailed past at the moment when I could see the road it takes, but was too far from the stop to get it. This covers the period when I am between around 50 and 10 yards from the bus stop.

Now the C2 comes roughly every 7 minutes. I timed how long it takes me to travel the distance over which I can see the bus but can't get on it. As luck would have it, the answer is 42.7 seconds.

7 minutes = 420 seconds.

420/42 = 10 42-second periods in which any one bus could go past.

This seems to mean that the chances of the bus going past in the particular period when it is most annoying four days in a row are (1/10)^4 = 1/10,000 (assuming my choice of 42-second period is random).

Is my maths wrong or are the bus gods against me?