Its easy to solve this problem by taking 100 as the cost price of the sweater.
If it is marked up 70%, the selling price is 70% more than 100, which is 170 as shown below:
Selling price = 

Now we need to subtract 25% of 170 from 170 to get his new price (at which he sold).
New price = 

He sold it for $127.5. So how much profit did he make?
Profit = Income - Cost = 
 dollars
 dollars
In percentage, 
 %
%
ANSWER: 27.5% profit