Puzzle 116 - Solution

1.  When the dealer gives you a discount of 15%,  amount will be x (1-0.15) = 0.85x
• Then when he takes a commission of 10%, his commission will be 0.085x
• The final amount you will pay  is 0.85x + 0.085x = 0.935x 
2. When the dealer first takes a commission of 10%, amount will be 1.1x
• When he gives a discount, discount amount will be 1.1*0.15x = 0.165x
• The final amount you pay will be 1.1x - 0.165x =  0.935x

For you, both the options are equal.

 

For the dealer - 

1.  If he takes a commission after discount, his commission will be 0.085x = 8.5%
2.  If he takes commission before discount, his commission will be 10%

So for the dealer second option is more profitable.