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?

12 6 9 3

3

3 humans, Cats : Dogs = 1 : 2 ⇒ Humans have 2 legs, cats and dogs have 4 legs each, therefore, ⇒ 3(2) + a(4) + 2a(4) = 42 ⇒ 6 + 4a + 8a = 42 ⇒ 12a = 42 - 6 ⇒ 12a = 36 ⇒ a = 3, Therefore there are = 1 x 3 = 3 cats.