Answer:
68%
Step-by-step explanation:
The mean is 25 and the standard deviation is 5. Â So 20 is one standard deviation below the mean and 30 is one standard deviation above the mean.
According to the Empirical Rule, 68% of the normal curve is between ±1 standard deviations.  So the answer is 68%.
Answer:
The correct option is 2.
Step-by-step explanation:
Given information: The population mean is μ=25 and standard deviation is σ=5.
[tex]Z=\frac{X-\mu}{\sigma}=\frac{X-25}{5}[/tex]
We need to find the percent of the trees that are between 20 and 30 years old.
[tex]P(20<X<30)[/tex]
Subtract 25 from each side.
[tex]P(20-25<X-25<30-25)[/tex]
[tex]P(-5<X-25<5)[/tex]
Divide each side by 5.
[tex]P(-1<\frac{X-25}{5}<1)[/tex]
[tex]P(-1<Z<1)=P(Z<1)-P(Z<-1)[/tex]
Using standard normal table we get
[tex]P(-1<Z<1)=0.84134-0.15866=0.68268\approx 0.68=68\%[/tex]
68% of the trees are between 20 and 30 years old.
Therefore the correct option is 2.
