>Let B = base amount = $500
> T = tax amount = $74.88
> F = Federal tax % = 5
> P = Provincial tax % = 9.5
>
>
>if we know T, F and P then B can be derived as follows:
>
> B = (T*100) / ( F + P + (F*P)/100)
>
>Having derived B you can the calculate the Federal tax amount as B * (F/100)
>and the Provincial Tax amount as B * (1+(F/100)) * (P/100)

Thanks

This is close but does not give the exact amount:

(74.88*100) / ( 5 + 9.5 + (5*9.5)/100)

...gives 500.03$

I tried something like that last night but was never able to obtain the exact number.