In the PS section of the article. There is a formula for %change. A close look of the numbers reveals some inconsistencies in the use old old number versus new number. The article is here http://www.manhattangmat.com/strategy-series-intuition.cfm
Could you please tell us the correct formula. I think it is ..
(old value -new value)/old value.[/url]

the formula is correct but there seems typos while putting the values in the link:

the formula for the % change = [new value - old value] / old value

Hmm - something's not right there. I'll alert our curriculum director.

The way we really want to use the formula is:
larger number minus smaller number
over original number

Otherwise, you can end up with a negative number - what we really care about on the numerator is the difference between the two numbers.

So the easiest formula to remember is:
change / original

Then you don't have to keep straight what you subtract from what - just what's the difference? And put that over the original.

Thanks for the reply Stacey. I checked a practice problem from the student center, and it has the right formula you have indicated.

You're welcome!