



 
Hi Jilly, Here in Canada the GST is 5%. Suppose that the price before the GST is $B, the price after is $A and the tax rate is r. (In your example $A = $500 and r = 0.10.) If you know the before price and the tax rate then, as you said, you just add the tax
or
To find $B you divide both sides by 1 + r to get
Thus in your example with $A = $500 and r = 0.10
I hope this helps,  


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