Do you understand this:?

Question

If y varies directly as X and y = 5 when X = 3 find Y when X = 18 and another Y = 1/5 and X = 20 then find Y when X = 2

I am so lost!

Answer 1

okay for the first one i dont know if its right bu if Y = 5 and X = 3 then I would say Y = 30 when X = 18 cause 3 x 6 = 18 and u have to do to Y what u did to X so it would be 5 x 6 = 30.

Answer 2

If y varies directly as y, this means that however much x goes up or down, y will too.  If you double x, y will double.  If you divide x by a third, y will also be divided by a third.

y = 5 when X = 3 find Y when X = 18

You can solve this by setting up a ratio

x/y = 3/5 = 18/?

To get from 3 to 18, x was multiplied by 6.

To keep the same ratio, y also has to be multiplied by 6.

y = 5*6 = 30

Y = 1/5 and X = 20 then find Y when X = 2

You divide x by 10 to get from 20 to 2.

Do the same to y.

1/5 ÷ 10 = 1/5 * 1/10 = 1/50

I hope that helps.

Answer 3

"y varies directly as x" means that when you increase x by a certain factor, you increase y by the same factor.  Double x, you double y.  Multiply x by 10, you multiply y by 10 as well.  This is expressed mathematically as

y = kx

where k is some constant.

In your first problem, you multiply x by 6 to go from 3 to 18.  So we multiply y by 6 and go from 5 to 30.

Do the other one the same way.