y = 18, when x = 5

Question

Given the values of x and y, find an equation of variation in which y varies directly as x.

Answer 1

Since y varies directly as x, y = kx, for some constant, k.

 

Find k:  y = 18 when x = 5, so 18 = 5k

 

                                             k = 18/5 = 3.6

 

The equation of variation is:  y = 3.6x

Answer 2

A direct variation is in the form

y = kx

 

18 = 5k          divide both sides by 5

18/5 = k

 

y = 18x/5