For a man who weighs 80 kg and is 1.80 m tall, the BMI is approximately 24.7. A weight of 79.5 kg and the same height yields approx. 24.537, while a weight of 80.5 kg yields approx. 24.846. Since the function is monotonically increasing, we conclude that the true BMI is in the range formula_20. Since the entire range is less than 25, which is the cutoff between normal and excessive weight, we conclude that the man is of normal weight.