which is a better deal on a $399.99 item: 50% off original price or 40% off and addtional 20% at the register?

Price you pay is : 399.99 - 50%  =   399 x .5  =

 

40% off means you pay 60% of original      then 20 % more off means you py 80% of THAT price

 

Price you pay is  :   399.99 x  .6   x .8   =        You can do the calcs and see which is better   (they are close to the same)