Question

In which equation is the constant of proportionality 5?

A. x=5y

B. y=5x

C. y= x+5

D. y=5-x

Answer 1

The constant or proportionality is in the equation: 
y = kx

Where 'k' is the constant of variation or the proportionality. 

y = 5x would demonstrate this. 

Answer: B. y=5x

Answer 2

Answer: B. y=5x

Step-by-step explanation:

We know that the rate of change which is also known as the constant of proportionality ($c=\frac{y}{x}$) which is the constant ratio between two proportional quantities .

Let's find constant of proportionality in all of the given options:

A.  x=5y

$\Rightarrow\ \frac{y}{x}=\frac{1}{5}\neq5$

B.y=5x

$\Rightarrow\ \frac{y}{x}=5$

C. y=x+5

$\Rightarrow\ \frac{y}{x}=\frac{x+5}{x}\neq\text{constant of proportionality}$

D.y=5-x

$\Rightarrow\ \frac{y}{x}=\frac{5-x}{x}\neq\text{constant of proportionality}$

Thus, in B the constant of proportionality is 5.