Dominic Ralph and Peter have just eaten a huge Christmas meal Dominic now weighs half as much as Ralph and Peter weighs three times as much is Dominic together they weigh 720 pounds how much does Dominic go away

Dominic+Ralph+Peter=720

so substituting in what we know (X stands for Ralph)

1/2X+X+3 (1/2X) = 720

simplify to

1/2X+1X+7/2X=720

get every coefficient on X with a denominator if 2 (so they can be added together wih least common denominators)

1/2X+2/2X+7/2X=720

add the left side of the equation up

10/2X=720

simplify

5X=720

divide five from both sides

X=144

recall that Ralph=X=144 pounds

Dominic=1/2 (Ralph) = 1/2 (X) = 1/2 (144) = 72 pounds

Peter=3 (Dominic) = 3 (72) = 216 poubds

Ralph=144 pounds

Dominic=72 pounds

Peter=216 pounds

Dominic 160 pounds

Ralph 80 p

Peter 480p