鸡的只数与其他两种家禽的只数比是1:4
显然,鸡占了总数的1/(1+4) = 1/5
鸭与其他两种家禽的只数比是2:5
显然,鸭占了总数的2/(2+5) = 2/7
则总数 = 2520 ÷ [2/(2+5)] = 8820只
鸡 = 8820 * 1/5 = 1764只
鹅 = 8820-1764-2520 = 4536只
鸡的只数与其他两种家禽的只数比是1:4
显然,鸡占了总数的1/(1+4) = 1/5
鸭与其他两种家禽的只数比是2:5
显然,鸭占了总数的2/(2+5) = 2/7
则总数 = 2520 ÷ [2/(2+5)] = 8820只
鸡 = 8820 * 1/5 = 1764只
鹅 = 8820-1764-2520 = 4536只