# Thread: probability problem with standard deviation & mean.

1. ## probability problem with standard deviation & mean.

The weights of adult long-tongued fruit bats are known to be normally distributed with a mean of 20.22 grams and a standard deviation of 3.23 grams. What is the probability that a randomly selected bat will:
a) weigh at most 15 grams?
b) weigh less than 30 grams?

2. ## Re: probability problem with standard deviation & mean.

Do you have a scientific calculator?

yes

4. ## Re: probability problem with standard deviation & mean.

Do you have access to a Q function table and know how to use it? If the random variable X has the mean $\mu$ and standard deviation $\sigma$, then $F(X \leq x)=Q\left(\frac{x-\mu}{\sigma} \right)$

The two questions basically ask the same thing with different wording (just replace x in the formula).

5. ## Re: probability problem with standard deviation & mean.

Under distribution on the calculator
normalcdf (left minimum, right maximum, mean, stand dev )
Use -10000 for far left and 10000 for far right so that you get all the area that you can under the normal distribution.
Example: for B normalcdf(-10000,30,20.22,3.23)