How can you determine the total cost of an item including tax?

Answer 1

There are two equivalent way.

Suppose the item costs C units (of whatever currency),

and suppose the tax rate is R %.

You calculate the total tax = C*R/100 currency units

so total costs = C + C*R/100

Alternatively, you calculate the tax multiplier, = (1 + R/100)

and then the total cost is C*(1 + R/100).

It is simple to show the two arrive at the same answer.