4 years 
6000 x .3 = 1,800. 1800 divided by 450 = 4
        
             
        
        
        
Answer:
A  99% confidence interval  will be wider than a 95% confidence interval 
Step-by-step explanation:
From the question we are told that 
   The  95% confidence interval for for the mean foot length for students at the college is found to be 21.709 to 25.091 cm
Generally the width of a confidence interval is dependent on the margin of error.
Generally the margin of error is mathematically represented as  
      
From the above equation we see that 
           
 
Here  
  is the critical value of the half of the level of significance and this value  increase as the confidence level increase
Now if a  99% confidence level is  used , it then means that the value of  
  
  will increase, this in turn will increase  the margin of error and in turn this will increase the width of the confidence interval 
Hence a 99% confidence interval  will be wider than a 95% confidence interval 
 
        
             
        
        
        
Answer:
C. y +3 = x +3
Step-by-step explanation:
We need to find in below option x has direct variation with y.
We solve for each;
A. 
From above equation we can state that 2 times y is equal to 7 less than 3 times of x.
Hence it doesn't represent direct variation.  
B. 
Solving above expression we get;

From above equation we can state that y is equal to 10 more than x.
Hence it doesn't represent direct variation. 
C. 
Solving above expression we get;

From above equation we can state that y is equal to x.
Hence it represent direct variation. 
D. 
Solving above expression we get;

From above equation we can state that 4 times y is equal to 2 less than 4 times of x.
Hence it doesn't represent direct variation. 
Hence the Answer which represent direct variation of x and y is,
C. 
 
        
             
        
        
        
The answer to this question is b