I've noticed my TI-calculator has been given me these strange answers. I'm sure I did the problem right:
"Biologists are studying a starfish population. The mean starfish length is 18 cm with a standard deviation of 7 cm. If a sample of 49 starfishes are randomly selected, what is the probability that the sample's mean is between 15 to 20 cm?"
I got normalcdf(15,20,18,1) = 0.97589, but when I did normalcdf(-3,3) I got 0.9973. Can someone help me figure out what happened? I standardized it and got a different area which shouldn't happen.
Steps:
$P(15 < X < 20) = normalcdf (15,20,18,1)$ $P\left(\frac{(15-18)}{1} < Z < \frac{20-18}{1}\right) = P(-3 < Z < 3) = normalcdf(-3,3)$
