Question

Mary bought a shirt on sale for $15. The sales tax was 10%. It's Mary played with a $20 bill, what was her change.

Answer 1

The equation is:

$20 - ($15 x 1.10) = x

It would cost $16.50 because the sales tax makes the price 110% of what it used to be or 1.1 times more.

Now you have 20 - 16.5 = x

20 - 16.5 = 3.5.

She got $3.50 in change.

Hope this helps :)