Answer:
a.1.90 years
Step-by-step explanation:
We have that to find our 
level, that is the subtraction of 1 by the confidence interval divided by 2. So:
Now, we have to find z in the Ztable as such z has a pvalue of 
.
So it is z with a pvalue of 
, so 
Now, find the margin of error M as such
In which 
is the standard deviation of the population and n is the size of the sample.
In this question:
So
So the correct answer is:
a.1.90 years
Answer:
Subtract 8.5
Step-by-step explanation:
To solve the equation, y has to be isolated (only y will be on one side of the equation)
To do this, we have to get rid of the 8.5, so it has to be subtracted from both sides.
So, the correct answer is subtract 8.5
Y=24 Y-12=12 Y=12+12 Y=24
(X-12) = 12
X = 12+12
X=24
