Answer:
68%
Step-by-step explanation:
The mean is 25 and the standard deviation is 5. 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.
