In the united states, birth weights of newborn babies are approximately normally distributed with a mean of μ = 3,500 g and a standard deviation of σ = 500 g. what percent of babies born in the united states are classified as having a low birth weight (< 2,500 g)? explain how you got your answer. the z-score for 2,500 g is –2. according to the empirical rule, 95% of babies have a birth weight of between 2,500 g and 4,500 g. 5% of babies have a birth weight of less than 2,500 g or greater than 4,500 g. normal distributions are symmetric, so 2.5% of babies weigh less than 2,500g.