A group of people,dogs, and birds has seventy legs, thirty heads, and twenty
tails. How many cats are among this group? (Assume all birds have two legs and a tail.)	Choose the correct choice from the following choices.
A) 0 B) 5 C) 13 D) 15 E) 20
Write P, C, and B for the number of people, dogs, and birds respectively, so that   we have   2P + 4C + 2B = 70, P + C + B = 30,C + B = 20:   Comparing the last two equations we obtain P = 10, and the first equation simplifies to   4C + 2B = 50, or 2C + B = 25. Therefore,   C = (2C + 5) -(C + 5) = 25- 5 = 5   correct answer 5
<result>B</result>
A group of people,dogs, and birds has seventy legs, thirty heads, and twenty
tails. How many cats are among this group? (Assume all birds have two legs and a tail.)