sunsun2z16 wrote:From 2003 to 2004 the profits made by a company increased by 10%. A year later in 2005, the profits of this company decreased to their 2003 value. By what percent did the profits decrease from 2004 to 2005? 

A) 10 
B) 5 
C) 1 
D) 20 
E) 9

Let's test some values.
Let's say the 2003 profits are $100
After a 10% increase, the 2004 profits are $110
In 2005, the profits are back to $100

So, we're going from $110 to $100

Percent decrease = 100(change)/original value
= 100(110- 100)/110
= (100)(10)/110
≈ 9.1%

Related Video: https://www.gmatprepnow.com/module/gmat ... video/1078

Hi sunsun2z16,

It looks like each of the explanations has properly explained the 'math' behind this question (and how to TEST VALUES to quickly get to the correct answer), so I won't rehash any of that here. Instead, I'm going to point out the relative importance of knowing all of the necessary formulas and math rules that you'll be expected to use on Test Day. Here, the concept is "percent change", which is a rather important formula in the realm of business - and you'll be asked to use it at least once on the Official GMAT. That formula can be defined in a couple of different ways:

Percent Change = (New - Old)/Old = (Difference)/Original

The key to using this formula is make sure that you clearly define the 'old' value and the 'new' value. As long as you do that, then the calculations involved are almost always fairly straight-forward.

GMAT assassins aren't born, they're made,
Rich