Final answer:
The constant of proportionality k in the directly proportional relationship between x and y, where y = 5 when x = 4, is found to be 1.25, and the equation is y = 1.25x.
Step-by-step explanation:
Given that there is a directly proportional relationship between two quantities, x and y, and knowing that when x = 4, y = 5, we can write the equation of direct proportionality as y = kx, where k is the constant of proportionality.
To find the value of k, we use the given values of x and y:
Then we solve for k:
Therefore, the constant of proportionality k is 1.25, and the equation representing this direct relationship is y = 1.25x.
Complete question:
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There exists a direct relationship between two quantities, x and y, such that when x = 4, y = 5. Write an equation and find k, the constant of proportionality for this relation.