Question

A temporary coffer dam is to be built to protect the 5 year construction activity for a major cross valley dam. If the coffer dam is designed to withstand the 20 year flood, the risk that the structure will be over topped in the third year exactly is ______ (in percentage)

• A. 4.51

Answer 1

The correct option is A 4.51
Probability of occurrence
$p=\frac{1}{T}=\frac{1}{20}$

Probability of non-occurrence
$q=1-p=1-\frac{1}{20}=\frac{19}{20}$

$\therefore$ Risk that the structure will be over topped in the third year exactly

$=q\times q\times p$

$=\frac{19}{20}\times \frac{19}{20}\times \frac{1}{20}$

$=0.0451$

$=4.51\%$