Question

Dominic, Ralf and Peter have just eaten a HUGE Christmas meal. Dominic now weighs half as much as Ralf, and Peter weighs three times as much as Dominic. Together they weigh 720 pounds. How much does Dominic weigh?

Answer 1

Dominic is 120 pound's, Ralf is 240 pound's, and Peter is 360 pound's. (I know you only asked for Dominic but i felt like giving you the other's to).:3 

Answer 2

To be able to calculate the problem above, we need to set up equations. We let,

D = Dominic weight
R = Ralph weight
P = Peter weight

We have three unknowns so we should set up three equations. We do as follows:

D = 0.5R
P = 3D
D+R+P = 720

Solving simultaneously we obtain,

D = 120
R = 240
P = 360

Therefore, Dominic weighs 120 mass units.