In article m, Roland
Perry writes
How likely is it for two Circle Line trains to be within a minute of
each other at KXSP between 8:30 and 9:00 in the morning?

If the former, it's extremely unlikely. If the latter, it's very
likely. (Noting that perhaps one in six trains on the tracks are likely
to be Circle rather than Metropolitan or H&C).

More like one in four. The trains are supposed to be 2 minutes apart,
and there are 7 Circles with a circulation time of 50 minutes. So 7
trains in 25 are Circles.

In 30 minutes there are 15 arrivals on each line. Probably 4 on (say)
the Inner Rail are Circles. So the probability of there also being a
Circle on the Outer Rail at the same time as a given one of these is
4/15, and the probability of one of the four getting a coincidence is
roughly 1 - (1 - 4/15)^4, or about 0.7. [Yes, that simplifies some
issues.]

--
Clive D.W. Feather | Home:
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