# Homework Help: Find the percentage increase in y

1. Nov 5, 2006

### topsyturvy

y is directly proportional to x2.
x is increased by 100%.
Find the percentage increase in y.

so,
y=k x2

y= k (100 + x2)
then i went to find the k,
which is
k= y/ (100 + x2)

so i put back the k which i found into y= k (100 + x2)
which is :
y= y/(100 + x2) (100 + x2)

them im stuck here..:yuck:
somebody pls helppp!
thanks lotsa.

2. Nov 5, 2006

it should be $$4x^{2}$$ not $$x^{2} + 100$$

Last edited: Nov 5, 2006
3. Nov 5, 2006

### VietDao29

x is increased by 100% just means that x has been doubled (i.e: 2x), and not 100 + x. Do you see why?
Consider the original amount (say b) to be 100%, so when increasing the original amount (i.e increase b) by 100% means that you add one more b to your original b, and get 2b, right?
So, can you go from here? :)
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@courtrigrad: No, it should be 4x2, not 2x2.
EDIT: He did edit the post. Cheers. :)

Last edited: Nov 5, 2006