Friday
May 6, 2016

# Homework Help: math

Posted by simon on Sunday, April 15, 2007 at 6:19am.

can anyone help please, i need a simple formula for working out taxes.if i had any number i need to know what the base was before 16% tax was added.
i know the formula if the tax was 17.5%,what ever the total is if you divide that by 47 then x that by 7 that will give you the base before tax was added.
example 50 divide 47 x 7 = 7.44

this gives me the total tax i paid if the rate was 17.5% , i need to know a similar formula if the tax is 16%,thanks.

why bother with a "formula"?

If you have the total after 17.5% tax was added, that total must represent 117.5% of the original.
So if you divide your total by 1.175, which is 117.5%, you get the original.
Now multiply that by .175 and you have the amount of the tax.

so \$50÷1.175x.175 = \$7.45

(notice 1.175/.175 = 1175/175 = 47/7 )

\$50÷1.16 x .16 = .....

.16/1.16 = 4/29

So your formula would be "divide by 29 then multiply by 4"

for 12% it would be .12/1.12 = 3/28

etc.

Personally, I would never use such a "formula", just do the math by reasoning it out.