Question

2: The age of trees in a forest is known to be approximately normal with an average age of 40 years and a standard deviation of 10 years. About ____ of the trees have ages between 10 years and 70 years.

Answer 1

Let's write the information we have and then start solving the problem.

We know that age is normally distributed so:

Now we have to calculate the p-values for the values 70 and 10 so:

And we know that the p-value for a z=3 is 0.9987.

Now:

And we know that the p-value for a z=-3 is 0.0013.

So the percentage of threes have ages between 10 years and 70 years is:

Percentage = 0.9987 - 0.0013

Percentage=0.9974

Percentage=99.7%

The answer for the question is A.