Jasper sold one set of barbells for 99 euros (he’s Dutch, remember), and he made a 10% profit on the deal. He sold a second set for 99 euros, but this time he took a 10% loss. Counting the two sales together, did he gain, lose, or come out even?
Let x be the cost of the first set of weights.
Let y be the cost of the second set.
Let y be the cost of the second set.
Cost  +  profit  =  selling price 
x  +  0.10x  =  1.10x = €99 → x = €90. 
y  –  0.10y  =  0.90y = €99 → y = €110. 
The costs:  The selling prices: 

€90  €99  
110  99  
€200  €198 
So Jasper had an overall loss of €2.