Question

Cellus

Suppose that y varies directly with x
and y = 3 when x = 9. What is y
when x = 18?
y = [ ?
]


I really suck at these problems.

Answer 1

y = 6 when x = 18

Explanation:

The appropriate formula for this direct proportion is y = kx, where k is the constant of proportionality.

We know y = 3 when x = 9: 3 = k(9)

This yields k = 3/9, or k = 1/3

Then the formula is y = (1/3)x

and when x = 18, y = (1/3)(18) = 6

y = 6 when x = 18