HMMT-Nov 2018 guts, Problem 9

Farmer James has some strange animals. His hens have 2 heads and 8 legs, his peacocks have 3 heads and 9 legs, and his zombie hens have 6 heads and 12 legs. Farmer James counts 800 heads and 2018 legs on his farm. What is the number of animals that Farmer James has on his farm?

Solution: Note that each animal has 6 more legs than heads. Thus, if there are $n$ animals, then there are $6 n$ more legs than heads in total. There are $2018-800=1218$ more legs than heads in total, so there are $\frac{1218}{6}=203$ animals. $\fbox{203}$.

Answer: 203