设鸡有X只,兔有（100-X）只.2X+4(100-X)=3162X+400-4X=3164X-2X=400-3162X=84X=84÷2X=42兔=100-X=100-42=58只答：鸡有42只,兔有58只.
42只鸡58只兔
