The ages of trees in a forest are normally distributed with a mean of 25 years and a standard deviation of 5 years.

Complete question is in comment section :

68%

Step-by-step explanation:

Mean = 25

Standard deviation = 5

The percentage of trees between 20 and 30

20 trees = 1 standard deviation below the mean ; mean - 1(standard deviation)

25 - 5 = 20

30 trees = 1 standard deviation above the mean ;

Mean + 1(standard deviation) ;

25 + 5 = 30

This means, 20 and 30 lies ±1 standard deviation from the mean which according to the empirical rule is 68%

According to the empirical rule :

thats not a system of equations, that is a solution

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