**Exceedance_P = P{X≥200} = 1 - P{X<200} = 1 - F(200) = 1 - 0.975 = 0.025**

*Note: F(200) is the CDF at 200.*

To obtain the return period (also known as the recurrence interval) of the event, we should calculate the reciprocal of the exceedance probability:

**Return_Period = 1 / Exceedance_P = 1 / 0.025 = 40 years.**

F(x) is CDF

The interpretation is that in a very long series, the 40-year flood value would be exceeded every 40 years on the average. For example, about twenty-five 40-year floods can be expected during a 1000 year period (on the average).

Source: http://www.mathwave.com/applications/flood_frequency.html

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