The weights of male babies less than 2 months old in the United States is normally distributed with a mean of 11.5 pounds and a standard deviation of 2.7 pounds.

Find the 80th percentile score for these weights.

I don't have a table, I have to figure it out using the TI-84 calculator and I don't know where to go with that.

1 answer

Don't have a TI-84 calculator, but....

Z = (score-mean)/SD

Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability (.80) related to a Z score. Insert that value into the above equation to find the score.