# math

posted by Jane

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.

1. Steve

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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