<span>y^2 + 5y + 6
=</span><span>(y + 2)(y + 3)
----------------------------------</span>
        
                    
             
        
        
        
Answer:
 --- Standard deviation
 --- Standard deviation
Step-by-step explanation:
Given
See attachment for graph
Solving (a): Explain how the standard deviation is calculated.
<u>Start by calculating the mean</u>
To do this, we divide the sum of the products of grade and number of students by the total number of students;
i.e.

So, we have:



Next, calculate the variance using the following formula:

i.e subtract the mean from each dataset; take the squares; add up the squares; then divide the sum by the number of dataset 
So, we have: 



Lastly, take the square root of the variance to get the standard deviation


 --- approximated
 --- approximated
<em>Hence, the standard deviation is approximately 11.28</em>
Considering the calculated mean (i.e. 82.76), the standard deviation (i.e. 11.28) is small and this means that the grade of the students are close to the average grade.
 
        
             
        
        
        
Answer:
24 hours
Step-by-step explanation:
The computation of the number of hours taken by Bobby to build the robot by himself is shown below:
Given that 
Bobby could take 12 hours
Together they could build in 8 hours
So based on the above information 
 the number of hours taken by Bobby to build the robot by himself is 
Let us assume the above line be x
So, 

x = 24 hours
 
        
             
        
        
        
0.2 is a decimal between 0.25 and 0.125
        
             
        
        
        
4/x = 6/(x+3)
6x = 4(x+3)
6x = 4x + 12
2x = 12
  x = 6
P = (4 + 6) +(6+3) + 6
P = 10 + 9 + 6
P = 25