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 120 pounds

WORKINGS

Let Dominic’s weight be represented by ‘D’
Let Ralf’s weight be represented by ‘R’
Let Peter’s weight be represented by ‘P’

Given,
Dominic now weighs half as much as Ralf;
D = ½ R
R = 2D                ….. (Equation I)

Peter weighs three times as much as Dominic;
P = 3D                ….. (Equation II)

Together they weigh 720 pounds
D + R + P = 720 pounds                ….. (Equation III)

How much does Dominic weigh?
D is unknown?

Substitute equation I (R = 2D) for the value of R in equation III
D + R + P = 720 pounds                ….. (Equation III)
D + 2D + P = 720 pounds
3D + P = 720 pounds                ….. (Equation IV)

Substitute equation II (P = 3D) for the value of P in equation IV
3D + P = 720 pounds                ….. (Equation IV)
3D + 3D = 720 pounds
6D = 720 pounds
D = 720/6 pounds
D = 120 pounds

Therefore, Dominic weighs 120 pounds.