A farmer keeps three types of animals on his farm: cows, pigs and horses. Can you guess how many of each animal he has based on the following information?

1) Three of the animals are NOT cows

2) Four of the animals are NOT pigs

3) Five of the animals are NOT horses

Answer: 3 cows, 2 pigs and 1 horse.

EXPLANATION: You can use algebra to solve the problem:

1) Pigs + Horses = 3

2) Cows + Horses = 4

3) Cows + Pigs = 5

Use the first two equations and isolate for Horses:

Horses = 3 - Pigs

Horses = 4 - Cows

therefore 3 - Pigs = 4 - Cows

Replace Cows in the above equation with 5 - Pigs (from equation 3):

3 - Pigs = 4 - (5 - Pigs)

3 - Pigs = 4 - 5 + Pigs

3 - Pigs = -1 + Pigs

4 = 2 x Pigs

Pigs = 2

Replacing Pigs with 2 in equations 1 and 3 will give you the number of Horses and Cows.

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