Probability of failure question?

1. The problem statement, all variables and given/known data
"The compressive strength of a concrete specimen follows a normal distribution with a mean value of 2.8 ksi and a coefficient of variation (COV) of 0.1. If the applied stress is 2.5 ksi, find the probability of failure."


2. Relevant equations
normal distribution formular


3. The attempt at a solution
I got the variance to be .28 ksi but i don't know how to find the probability of failure without knowing the maximum failure stress of the specimen. Can anyone help me out?
 
1. The problem statement, all variables and given/known data
"The compressive strength of a concrete specimen follows a normal distribution with a mean value of 2.8 ksi and a coefficient of variation (COV) of 0.1. If the applied stress is 2.5 ksi, find the probability of failure."


2. Relevant equations
normal distribution formular


3. The attempt at a solution
I got the variance to be .28 ksi but i don't know how to find the probability of failure without knowing the maximum failure stress of the specimen. Can anyone help me out?
Since the applied compressive stress is 2.5ksi you need to calculate the probability that the compressive strength will be below this value. From MS Excel I estimate this should be 14.2%.
 

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