Using the normal distribution, we have that:
a) The sketch of the situation is given at the end of this answer.
b) The probability is:
[tex]P(2.8 \leq X \leq 7) = 0.8284[/tex]
In a normal distribution with mean and standard deviation , the z-score of a measure X is given by:
[tex]Z = \frac{X - \mu}{\sigma}[/tex]
In this problem:
Item a:
The part between 2.8 and 7 years is shaded on the sketch given at the end of this answer.
Item b:
The probability is the p-value of Z when X = 7 subtracted by the p-value of Z when X = 2.8, thus:
X = 7:
[tex]Z = \frac{X - \mu}{\sigma}[/tex]
[tex]Z = \frac{7 - 4.1}{1.3}[/tex]
[tex]Z = 2.23[/tex]
[tex]Z = 2.23[/tex] has a p-value of 0.9871.
X = 2.8:
[tex]Z = \frac{X - \mu}{\sigma}[/tex]
[tex]Z = \frac{2.8 - 4.1}{1.3}[/tex]
[tex]Z = -1[/tex]
[tex]Z = -1[/tex] has a p-value of 0.1587.
0.9871 - 0.1587 = 0.8284, thus:
[tex]P(2.8 \leq X \leq 7) = 0.8284[/tex]
A similar problem is given at https://brainly.com/question/25151638