Quote Originally Posted by Yunie
y is inversely proportional to x^2.

So, there should be a constant. krtxmrtz use it as 'k' and he clearly solved it out, normally called as proportional constant. In mathematics by word you can say it as,

Two quantities are proportional, if they vary in a way that one quantities is a constant multiple of the other quantities.
Depend on that, logically solve the problem as follows. When the x goes to halved of the original the constant going to be halved. On you question it is change quadratically, so the constant going to be one-fourth. If it is going to inversely proportional, constant going to be 4, think in other way round. So to get the new value multiply the original value by 4.

When you much familiar with this, so easy to solve these type of problems.