Answer:
Z=-2
This value means that the score of Rachel 550 it's 2 deviations below the mean of the population  
Step-by-step explanation:
1) Previous concepts
Normal distribution, is a "probability distribution that is symmetric about the mean, showing that data near the mean are more frequent in occurrence than data far from the mean".
The Z-score is "a numerical measurement used in statistics of a value's relationship to the mean (average) of a group of values, measured in terms of standard deviations from the mean".  
 represent the population mean for the Graduate Record Exam (GRE)
 represent the population mean for the Graduate Record Exam (GRE)
 represent the population standard deviation for Graduate Record Exam (GRE)
 represent the population standard deviation for Graduate Record Exam (GRE)
2) Solution to the problem
Let X the random variable that represent the Graduate Record Exam (GRE) of a population, and for this case we know the distribution for X is given by:
 
  
Where  and
 and  
We want to find the z score for a score of 550. And in order to do this we need to apply the formula for the z score given by:
 
If we apply this formula to our probability we got this:

So the answer for our case would be Z=-2
This value means that the score of Rachel 550 it's 2 deviations below the mean of the population  
 
        
             
        
        
        
Answer:
33 copies were paperback and 12 were hardcover.
Step-by-step explanation:
Let h represent the number of hardcover copies and p represent the number of paperback copies.
We know that the total number of copies was 45; this gives us the equation
h+p = 45
We know that each hardcover copy is 7 ounces; this gives us the expression 7h.
We also know that each paperback copy is 5 ounces; this gives us the expression 5p.
We know that the total weight was 249 ounces; this gives us the equation
7h+5p = 249
Together we have the system

We will use elimination to solve this.  First we will make the coefficients of the variable p the same; to do this, we will multiply the top equation by 5:

To eliminate p, we will subtract the equations:

Divide both sides by -2:
-2h/-2 = -24/-2
h = 12
There were 12 hardcover copies sold.
Substitute this into our first equation:
12+p=45
Subtract 12 from each side:
12+p-12 = 45-12
p = 33
There were 33 paperback copies sold.
 
        
                    
             
        
        
        
Answer:22
Step-by-step explanation:
10x2+1x2=
20+2
=22
 
        
                    
             
        
        
        
Answer: The unit rate is 3 centerpieces per hour
Step-by-step explanation:
18centterpieces/6hrs =3
 
        
             
        
        
        
Answer:
answer to what? free points?
Step-by-step explanation: