Can anyone please explain why when I use a Canon calculator with Tax + and Tax - buttons, the answer does not seem right when I make a calculation.

Example: Tax is set at 20%. Enter 100 press Tax+ (20%) answer = 120
Now if I enter 100 press Tax- (20%) answer = 83.33
I understood that 20% of 100 =20

Why is the answer not 80 when I deduct 20%?

If I use the procedure on the calculator 100 - 20 % = I get the answer 80

Which is correct?

Because a tax of 20% on $100 is $20 so the total is $120.

A tax of 20% on $83.33 would be $16.666 and the total would be $99.996 (rounded to $100)

It answers the question of what is the cost of an item taxed at 20% if the total is $100.