Question

鸡、兔共有脚1aa只，若将鸡换成兔，兔换成鸡，则共有脚86只．问：鸡、兔各有几只？

Answer 1

设鸡有x只，兔有（1他他-2x）÷4只，由题意得：
4x+（1他他-2x）÷4×2=13，
&nbs左;&nbs左; 4x+（1他他-2x）÷2=13，
&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左; 4x+5他-x=13，
&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左; 3x=13-5他，
&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左; x=33÷3，
&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左;&nbs左; x=12；
则兔有：（1他他-2×12）÷4=19（只）．
答：鸡有12只，兔有19只．