A household of three humans has cats and dogs in the ratio 1 : 2. If the total number of legs in the household is 42, what is the total number of cats in the household?

A household of three humans has cats and dogs in the ratio 1 : 2.

Let's assume the number of cats and dogs are 'y' and '2y' respectively.

If the total number of legs in the household is 42.

Legs of three humans + number of legs of cats + number of legs of dogs = 42

$$3\times2+y\times4+2y\times4 = 42$$ [As we know that human has two legs and each dog and cat has four legs.]

$$6+4y+8y = 42$$

12y = 42-6

12y = 36

y = 3

Total number of cats in the household = y = 3