Pets in ZOO

The zoo has a run for pets. There are chickens, pigs, and cows. Altogether, there are 20 heads and 60 feet. How many chickens and piglets are there?

Correct answer:

x =  10
y =  9

Step-by-step explanation:


x+y+1 = 20
2x+4y+4=60

x+y+1 = 20
2·x+4·y+4=60

x+y = 19
2x+4y = 56

Pivot: Row 1 ↔ Row 2
2x+4y = 56
x+y = 19

Row 2 - 1/2 · Row 1 → Row 2
2x+4y = 56
-y = -9


y = -9/-1 = 9
x = 56-4y/2 = 56-4 · 9/2 = 10

x = 10
y = 9

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