Combining Direct and Indirect Variations in Solving for Unknown Variables

[you878]

Homework Statement

s varies directly as r and inversely as t. s=10 when r=5 and t=3. What value of t will s=3 and r-4?

Homework Equations

Direct variation: y=kx; Indirect variation: y=k/x

The Attempt at a Solution

I tired s=kr=k/x and plugging in the given, but I could not get t in the end.

My real question is how to combine variations, meaning: because s varies directly AND inversely, how do you combine the variations?

 

[statdad]

Write everything as a single variation, using only one constant $k$ rather than two separate expressions.

 

[you878]

Got it, thanks.