Math CentralQuandaries & Queries


Question from melissa:

I need to know the amount of gst that was in the amount of 630.67? How do you figure this out? I don't need the amount of gst after, but the gst included?

Hi Melissa,

This is one of those unusual math questions where the answer depends on where you live. In Saskatchewan where I line there is a pst and a gst so the amount after tax includes them both. Since you live in Alberta where there is no PST the amount paid, $630.67 only includes the ticket price of the item and the 5% gst. If you knew the ticket price, the price before the gst then you would calculate the gst be

gst = 5 % of the ticket price

which is

gst = 0.05 × the ticket price.

Hence the price you paid is

the ticket price + 0.05 × the ticket price = 1.05 × the ticket price = $630.67.


the ticket price = $630.67/1.05 = $600.64.

The difference between the price you paid and the ticket price is the gst.


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