Question

Suppose that y varies directly with x, and y=4 when x=20. •(a) Write a direct variation equation that relates x and y.Equation: ___. •(b) Find y when x = 9.y = ____

Answer 1

If y varies directly with x, you can write the following general equation:

y = kx

where k is the constant of proportionality. With the given information in the statement of the question you can find the value of k.

if y=4 when x=20, then, you can replace these values into the previous equation and solve for k, just as follow:

4 = k·20 divide by 20 both sides

4/20 = k simplify the fraction left side

1/5 = k

(a) Hence, the equation is:

y = (1/5)x

(b) If x = 9, you obtain for y:

y = (1/5)(9) = 9/5