40% off your entire purchase is the same as 20% off each item, right?

I was shopping with my daughter recently and we were in a store that had signs everywhere announcing "40% off Your Entire Purchase".  

Some young (and not so young) ladies were at the checkout in front of us with 2 pairs of jeans.  One of them asked, "so it's 20% off each item right?" 

 The cashier said, "Yes, well... It's 40% off your entire purchase.  So yea, that's the same thing, yea, it's the same as 20% off each item."  

Hmmmm.  

Let's say the jeans were $50 each.  20% off of one pair would make them $40 each (or $80 total).

Let's try that with 40% off of your entire purchase.  Two pairs of jeans would cost $100.  40% off the entire purchase would make the total $60.  Think I'd rather have 40% off the total :).