Answer: D) Increase the sample size and decrease the confidence level.
Step-by-step explanation:
A reduced interval width means that the data is more accurate. This can only be achieved if the sample size is increased because a larger sample size is able to capture more of the characteristics of the variables being tested.
A smaller confidence interval will also lead to a reduced interval width because it means that the chances of the prediction being correct have increased.
What do you meen they are numbers
The numbers of new CDs is 30 and the old CDs is 21.
To solve this problem, we have to write a system of equations in which we would know the numbers of each types of CD she bought.
<h3>System of Equations</h3>
This is used to solve a series or complex of word problems in which we can represent in a mathematical statements;
- Let n represents numbers of new CDs
- Let u represents numbers of old CDs
The equations can be represented as

Let's take equation (i)
Making n the subject of formula

we can put equation (iii) into equation (ii)

Let's put the value of u into equation (i)

From the calculations above, the numbers of new CDs is 30 and the old CDs is 21.
Learn more on system of equations here;
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