Question

If y varies directly with x and

y = 21 when x = 3, find y if x = 5.
First, find the direct variation equation,
y = [ ? ]x

Answer 1

y = kx

21 = k*3

Now use that to find x as needed.

Or, since y/x is constant (k), you can find the new x without even finding k.

You want x such that

105/x = 21/3

Explanation: