Answer:
We can not state the exact probability that y will fall between 195 and 205
Step-by-step explanation:
* Lets explain how to solve the problem
- Regression model applies with f(30) = 100 and f(31) = 20
- The variance = 25
- An observation on y will be made for x = 5
- Suppose that the regression model is

∵ 
∵ 
∵ x = 5
∴ Y = 100 + 20(5) = 100 + 100 = 200
∴ Y = 200
- But the regression model is without error term 
∵ We do not know the probability distribution of y for each value
of x we only know the value of y at one value of x
∵ We know that the mean of distribution is 100 + 20x
∵ We know the variance of distribution is 25
∵ We don not know the shape of the distribution
- We can not find the exact value of probability of y without the
Normal error
and the regression model must be
to know that it has a normal distribution
∴ We can not calculate the exact value of probability of y
∴ We can not state the exact probability that y will fall between 195
and 205