posted by Sue on .
length of time in minutes required to complete exercises is distributed with a mean of 60 minutes and a std. deviation of 8 minutes. what percent will require between 60 and 76 minutes to complete the exercises? what percent of participants will require more than 72 minutes to complete th exercises? what percent will require between 50 and 72 minutes to complete the exercises?
Use z-scores and a z-table to find your percentages.
Let's look at the very last question and then see if you can figure out the other two questions.
Find two z-scores using this formula:
z = (x - mean)/sd
mean = 60
sd = 8
x = 50, 72
z = (50 - 60)/8 = ?
z = (72 - 60)/8 = ?
I'll let you finish the calculations.
Once you have the z-scores, check a z-table for the probability between those two scores. Once you have that value, convert to a percent.
I hope this will help get you started.