10. A person goes hunting in the jungle, and he discovers a pack of wolves, among which are some mutant wolves. It is known that this person has one head and two legs, an ordinary wolf has one head and four legs, and a mutant wolf has two heads and three legs. All the people and wolves together have 21 heads and 57 legs, then all the wolves (including mutant wolves) have $\qquad$ heads.
【Answer】 15
【Analysis】 Exam point: The Chicken and Rabbit in the Same Cage problem
First, remove one head and two legs for each person, the total number of wolf heads is 20, and the total number of legs is 55. Consider a two-headed, three-legged mutant wolf as 2 one-headed, 1.5-legged monsters; assuming all are regular wolves, there would be $20 \times 4 = 80$ (legs), with a difference of 80 $-55 = 25$ (legs); the difference between 4 legs and 1.5 legs is 2.5 legs, $25 \div 2.5 = 10$ (heads) of monsters, $10 \div 2 = 5$ (heads) of mutant wolves, $20 - 5 \times 2 = 10$ (heads), $10 + 5 = 15$ (heads)