The standard deviation is the square root of the variance...so that means the variance is the standard deviation squared.
2.3^2 = 5.29 <===
        
             
        
        
        
Let numbers of books be 'b' and numbers of CDs be 'c'
We can set up two equations:
Equation [1] ⇒ 

Equation [2] ⇒ 

We are solving for the number of books and the number of CDs bought
When we have two equations in terms of two different variables; 

 and 

, that we need to solve, then this becomes a simultaneous equation problem. 
First, rearrange Equation [1] to make either 

 or 

 the subject:


Then we substitute 

 into Equation [2]






Now we know the value of 

 which is 

, substitute this value into 

 we have 

Answer:
Numbers of books = 13
Numbers of CDs = 7
 
        
        
        
Answer:
the answer is 1/2 and then 3/4
 
        
             
        
        
        
Answer:
112
Step-by-step explanation:
180 - 40 - 28 = 112