# math

Y is directly proportional to the square of x.
Find the percentage increase in value of y when x is doubled

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1. Y=kx^2
When x is doubled
Y=(2x)^2
Therefore Y=4x^2

Percentage increase=(3kx^2)/kx^2 Ã—100%
=300%
Is it good?

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posted by ashiana
2. correct, except I would keep the k in the calculation

old y = k x^2
new y = k (4x^2)
change in y = 3k x^2
percentage change = 3k x^2/(k x^2) = 3
or 300%

e.g. enter 1 and 4 for the following applet,
http://www.marshu.com/articles/calculate-percentage-increase-decrease-percent-calculator.php

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posted by Reiny

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