A chicken eats 0.21 kg per day. How much grain does the chicken eat in 8 days

To find out how much grain the chicken eats in 8 days, multiply the amount of grain the chicken eats per day by the number of days: 0.21 kg/day * 8 days = <<0.21*8=1.68>>1.68 kg. Answer: \boxed{1.68}.