John has 3 bedroom doors and two outside doors to replace.  The outside doors cost $20 each to replace and the bedroom doors are half that cost.  How much does he pay in total?
The outside doors cost 2*$20=$<T>multiply(2, 20)=40
Each indoor door cost $20/2=$<T>divide(20, 2)=10.0
So all the indoor doors cost $10*3=$<T>multiply(10, 3)=30
That means the total cost is $40+$30=$<T>add(40, 30)=70
