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

=> 
Answer:
Noiccce
Step-by-step explanation:
Noiccce
Negative plus a negative is always positive. positive plus a positive is a positive. but if you have an positive plus a negative whatever sign has the bigger number thats the sign you'll use.
The correct length would be 2√ units