The option C) y = 15/x
a) y = 15 x is an example of direct variation, with proportionality constant = 15
b) is an example of linear variation (it is the equation of a straight line that does not pass through the origin)
c) y = 15/x => y*x = 15 = constant which is the characteristic of an inverse relation
d) y = x/15 is an example of an inverse relation, with proportion constant = 1/15  
        
                    
             
        
        
        
Its D 15+15+15= 45  so there for it will be 45                       
                                                             
        
             
        
        
        
156 dollars because 13 times 12 (months)
equals 156
        
             
        
        
        
SOLUTION
Given the question in the image, the following are the solution steps to answer the question.
STEP 1: Write the given set of values

STEP 2: Write the formula for calculating the Standard deviation of a set of numbers
![\begin{gathered} S\tan dard\text{ deviation=}\sqrt[]{\frac{\sum^{}_{}(x_i-\bar{x})^2}{n-1}} \\ where\text{ }x_i\text{ are data points,} \\ \bar{x}\text{ is the mean} \\ \text{n is the number of values in the data set} \end{gathered}](https://tex.z-dn.net/?f=%5Cbegin%7Bgathered%7D%20S%5Ctan%20dard%5Ctext%7B%20deviation%3D%7D%5Csqrt%5B%5D%7B%5Cfrac%7B%5Csum%5E%7B%7D_%7B%7D%28x_i-%5Cbar%7Bx%7D%29%5E2%7D%7Bn-1%7D%7D%20%5C%5C%20where%5Ctext%7B%20%7Dx_i%5Ctext%7B%20are%20data%20points%2C%7D%20%5C%5C%20%5Cbar%7Bx%7D%5Ctext%7B%20is%20the%20mean%7D%20%5C%5C%20%5Ctext%7Bn%20is%20the%20number%20of%20values%20in%20the%20data%20set%7D%20%5Cend%7Bgathered%7D)
STEP 3: Calculate the mean

STEP 4: Calculate the Standard deviation
![\begin{gathered} S\tan dard\text{ deviation=}\sqrt[]{\frac{\sum^{}_{}(x_i-\bar{x})^2}{n-1}} \\ \sum ^{}_{}(x_i-\bar{x})^2\Rightarrow\text{Sum of squares of differences} \\ \Rightarrow10332.7225+657.9225+18591.3225+982.8225+2740.52251+9731.8225+3522.4225+18319.6225+2878.3225 \\ +8163.1225+1417.5225+3925.0225+1321.3225+386.1225+5677.6225+2953.9225+3800.7225 \\ +3209.2225+2565.4225+10537.0225 \\ \text{Sum}\Rightarrow108974.0275 \\  \\ S\tan dard\text{ deviation}=\sqrt[]{\frac{111714.55}{20-1}}=\sqrt[]{\frac{111714.55}{19}} \\ \Rightarrow\sqrt[]{5879.713158}=76.67928767 \\  \\ S\tan dard\text{ deviation}\approx76.68 \end{gathered}](https://tex.z-dn.net/?f=%5Cbegin%7Bgathered%7D%20S%5Ctan%20dard%5Ctext%7B%20deviation%3D%7D%5Csqrt%5B%5D%7B%5Cfrac%7B%5Csum%5E%7B%7D_%7B%7D%28x_i-%5Cbar%7Bx%7D%29%5E2%7D%7Bn-1%7D%7D%20%5C%5C%20%5Csum%20%5E%7B%7D_%7B%7D%28x_i-%5Cbar%7Bx%7D%29%5E2%5CRightarrow%5Ctext%7BSum%20of%20squares%20of%20differences%7D%20%5C%5C%20%5CRightarrow10332.7225%2B657.9225%2B18591.3225%2B982.8225%2B2740.52251%2B9731.8225%2B3522.4225%2B18319.6225%2B2878.3225%20%5C%5C%20%2B8163.1225%2B1417.5225%2B3925.0225%2B1321.3225%2B386.1225%2B5677.6225%2B2953.9225%2B3800.7225%20%5C%5C%20%2B3209.2225%2B2565.4225%2B10537.0225%20%5C%5C%20%5Ctext%7BSum%7D%5CRightarrow108974.0275%20%5C%5C%20%20%5C%5C%20S%5Ctan%20dard%5Ctext%7B%20deviation%7D%3D%5Csqrt%5B%5D%7B%5Cfrac%7B111714.55%7D%7B20-1%7D%7D%3D%5Csqrt%5B%5D%7B%5Cfrac%7B111714.55%7D%7B19%7D%7D%20%5C%5C%20%5CRightarrow%5Csqrt%5B%5D%7B5879.713158%7D%3D76.67928767%20%5C%5C%20%20%5C%5C%20S%5Ctan%20dard%5Ctext%7B%20deviation%7D%5Capprox76.68%20%5Cend%7Bgathered%7D)
Hence, the standard deviation of the given set of numbers is approximately 76.68 to 2 decimal places.
STEP 5: Calculate the First and third quartile

STEP 6: Find the Interquartile Range

Hence, the interquartile range of the data is 116