Farmer Paul has 4 puppies. The mass of Puppy F is the same as the average mass of the 4 puppies. Puppy G weighs 2 kg less than the average mass of the 4 puppies. The mass of Puppy H is 10 kg more than the average mass of the 4 puppies. The mass of Puppy J is 12 kg. Find the total mass of the 4 puppies.
Let 1 u be the average mass of each puppy.

Total mass of 4 puppies
= 4 x 1 u
= 4 u

Mass of Puppy F = 1 u
Mass of Puppy G = 1 u - 2
Mass of Puppy H = 1 u + 10
Mass of Puppy J = 12 kg

Total mass of the 4 puppies
= 1 u + (1 u - 2) + (1 u + 10) + 12 
= 3 u - 2 + 10 + 12
= 3 u + 20

4 u = 3 u + 20
4 u - 3 u = 20

1 u = 20

Total mass of the 4 puppies
= 4 u
= 4 x 20
= 80 kg

Answer(s): 80 kg