# A very simple math problem

If the value of a stock (as in the stock market) went down one day by 10% and then it went up the following day by 10% what is the value now?

Possible answers:
- same as before going down 10%
- lower than before going down 10%
- higher than before going down 10%

Obviously, the rule is the same whether we are talking about a stock, a house, a car, a bicycle, a toy, etc.
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> Correct answer:
> - lower than before going down 10%
>
> This is because we calculate the increase in percent each day based on the previous day price. 
> So if price was:
>  $100 and went down 10% , price is $90
> if next day price went up 10% from $90 that's only $9 increase so value is $99 now after going 10% down one day and 10% up next day