Question

Determine the constant of variation for the direct variation given.

R varies directly with S. When S is 16, R is 80.


1/5
5
16

Answer 1

Varies directly means you have this kind of a relationship:

y = kx

where k is a constant number. In your problem ituses R and S, though. Whatever varies directly is basically your y in the formula above. So if R varies directly, I can put
R = kx
What y varies directly to is x. So in this case R varies directly to S, meaning x is S. SO now I can write
R = ks.
When s is 16, r is 80, so let's plug those in:

80 = 16k.

k is the constant of variation, so now just solve for k and that's your answer.

Any varies directly/varies jointly problem is set up like this

y = kx

Just pay attention to the question as it tells you what varies directly to what.