



 
Hi Lorrinn, Percent means "per 100" so 10% is 10/100 = 0.10. When you say 10% of $100 is $10 you are multiplying
When you say "on the inside" you don't know the amount (the $100 above), instead you know that whatever this number is, adding 10% gives a result of $100. The beauty of algebra lets me take the awkward previous sentence and write it more clearly. If you let x be the unknown amount then
In other words
or
Dividing both sides by 1.10 gives
That is part of the formula you use. You then take 10% of this number to get
I hope this helps,  


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