SOLUTION: y varies inversely with x. Write this statement as an equation in x,y and k,where k is constant. If x decreases by 20%, find the percentage change in y.

Question 934672: y varies inversely with x.
Write this statement as an equation in x,y and k,where k is constant.
If x decreases by 20%, find the percentage change in y.

Answer by Theo(13342) (Show Source): You can put this solution on YOUR website!
y = k/x is the equation for inverse proportion.

let y1 = k/x

let y2 = k/(.8x)

ratio of y2 to y1 = y2 / y1 = (k/.8x) / (k/x) = (k/.8x) * (x/k) = 1/.8 = 1.25

if x decreases 20%, then y increases 1/20% which is equal to 1.25 times.

example:

y = 200 when x = 100

y = k/x gets you k = 20,000.

x decreases by 10% makes x = 80.

y = 20,000 / 80 becomes y = 250.

250 / 200 = 1.25

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