John buys 500 newspapers.  Each newspaper sells for $2.  He sells 80% of them.  He buys them all for 75% less than the price at which he sells them.  How much profit does he make?
He sells 500*.8=<T>multiply(500, 0.8)=400.0 newspapers
He sells them for 400*2=$<T>multiply(400, 2)=800
He gets a discount of 2*.75=$<T>multiply(2, 0.75)=1.5 on the newspapers
So he buys them for 2-1.5=$<T>subtract(2, 1.5)=0.5
So he spent 500*.5=$<T>multiply(500, 0.5)=250.0 buying them
That means he made a profit of 800-250=$<T>subtract(800, 250)=550
