Answer:
The value is 
Step-by-step explanation:
From the question we are told that
The mean is 
The standard deviation is 
The safest water level is between 7.2 and 7.8
Generally the probability that the selected pool has a pH level that is not considered safe is mathematically represented as

Here

Generally 
So
=>
From the z-table the probability of (Z < -1.5) and ( Z <1.5) are

and

So
So

=> 
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Answer: c.
Step-by-step explanation:
As per given , we have
Total number of residents injured from roller-skating =1,800
Total number of deaths from roller-skating = 90
Formula for Mortality rate : 
Then, the proportional mortality ratio (%) due to roller-skating was
=
= 5%
Hence, the correct answer is c.
The answer is D +14 because to negatives make a positive
From -∞ to -4 the blue line is above the X axis which means it is >0
The blue line is negative between -4 and -3
This would make the correct answer: F(x) > 0 over the interval (-∞,-4)