Question

Y varies directly with x. y is 36 when x is 4. What is x when y is 81?

50 POINTS

Answer 1

x = 9

Explanation:

given y varies directly with x then the equation relating them is

y = kx ← k is the constant of variation

to find k , substitute y = 36 , x = 4 into the equation

36 = 4k ( divide both sides by 4 )

9 = k

y = 9x ← equation of variation

when y = 81 , then

81 = 9x ( divide both sides by 9 )

9 = x