Why do some coupons have Math Questions at the bottom that Canadian residence must answer?

Question

I have a coupon from Payless shoes and at the bottom it says, "Canadian residents only: To receive this discount, you must first correctly answer, unaided in any way, the math skill testing question below. Question: Add 42 + 16; then subtract 18; then multiply by 2; then divide by 10."

Answer 1

It is required by Canadian law in order to not be classed as an illegal lottery:

http://vancouverplus.workopolis.com/servlet/Content/fasttrack/20030524/RSKIL?section=Legal/

Hope this helps!