Thread: another variation

find the required value by setting up the general equation and then evaluating.

find y when x=10 if y varies directly as x and y=20 when x=8


thanks!

Originally Posted by mamajen

find the required value by setting up the general equation and then evaluating.

find y when x=10 if y varies directly as x and y=20 when x=8


thanks!

When y varies directly as x, we have the equation . The first thing to do is solve for k. Substituting in y = 20 and x = 8 we have , or .

Given that , can you determine y when x = 10?

yes i can get it from there. thanks. I was not thinking to find k first!

Icemanfan, hope you don't mind me just adding something.

mamajen, In the other question you asked, I said what "proportional" mean and told you about putting the k there and then working out what k was. Well, "varies directly as" just means "is proportional to", so the two questions are quite similar.

thanks iceman. i remembered that part but didn't know where to put all the equal to #'s. then when I saw he used the 2nd y= to find k I knew where I was going