Probability of a 10-year flood to occur at least once in the next 5 years is 

This question was previously asked in
ESE Civil 2015 Paper 2: Official Paper
View all UPSC IES Papers >
  1. 35%
  2. 40%
  3. 50%
  4. 65%

Answer (Detailed Solution Below)

Option 2 : 40%
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ST 1: UPSC ESE (IES) Civil - Building Materials
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Detailed Solution

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Concept:

The probability for the annual maximum flood magnitude to occur = \(\frac{1}{{Return\;period\;}} \)

Calculation:

Given,

Return period T = 10 years

 n = 5 years

p is the probability of occurring an event 

q is the probability of not occurring an invent.

\(\begin{array}{l} p = \frac{1}{T} = 0.1\\ q = 1 - p = 0.9 \end{array}\)

Probability of flood at least once in next 5 years

= 1 – no flood in next 5 years

= 1 – q5

= 1 – (0.9)5 = 0.40
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