Posted by **Jane** on Tuesday, November 6, 2012 at 1:37pm.

If y varies diretly with x, write an equation for the direct variation. then find each value.

Find y when x = 10 if y = 8 when x = 20

If think I can find the value by

y/10 = 8/20 with the answer for the value is 4. My problem is how to find the equation. Please explain.

- math -
**Steve**, Tuesday, November 6, 2012 at 2:24pm
what does "y varies diretly with x" nean?

It means that there is some constant k, such that y = kx.

so, knowing that 8 = k*20 (because they told us that y = 8 when x is 20), we see that k = 8/20, or 2/5.

Thus, y = 2/5 x

when x=10, y = 2/5 * 10 = 4

So, you got the right value for y, but you needed to review just what "y varies diretly with x" means.

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