John's weight bench can support 1000 pounds.  He wants to make sure to stay 20% under that weight for safety.  If he weighs 250 pounds how much weight can he put on the bar?
He wants to stay 1000*.2=<T>multiply(1000, 0.2)=200.0 pounds under the max
So he wants to stay under 1000-200=<T>subtract(1000, 200)=800 pounds
That means he can put 800-250=<T>subtract(800, 250)=550 pounds on the bar
