Answer:
We conclude that the constant of proportionality between the number of shirts and how much they cost is:
k = 8
Hence, option 'D' is correct.
Explanation:
We know that when 'y' varies directly with 'x', we get
y ∝ x
y = kx
k = y/x
where k is called the constant of proportionality
Given the points
For (10, 80)
substituting y = 80 and x = 10 in the equation
k = y/x
k = 80/10 = 8
For (20, 160)
k = y/x
k = 160/20 = 8
For (50, 400)
k = y/x
k = 400/50 = 8
It is clear that the value of k is the same for all the points.
Thus, the value of k = 8
Therefore, we conclude that the constant of proportionality between the number of shirts and how much they cost is:
k = 8
Hence, option 'D' is correct.