a Substitute the value of into the formula and evaluate.
B
b Substitute the value of into the formula and evaluate.
C
c What is the relation between and n?
A
a n>9
B
b n>891
C
c See solution.
Practice makes perfect
a We are given a formula that relates the percent of population with a certain characteristic and the number of people n to choose for a random sample so that it is representative for the particular population.
n>9(1-/)
Let's suppose that the percent of population with a characteristic of our interest is 0.5. To calculate the size of a representative sample we can substitute 0.5 for into the given formula and solve for n.
We should choose at least 9 people from the population to be in a sample.
b This time we are asked to suppose that the percent of population with a characteristic of our interest is 0.01. To calculate the size of a representative sample we can substitute 0.01 for into the given formula and solve for n.
We should choose at least 891 people from the population to be in a sample.
c Let's summarize the results from parts A and B.
Least Reasonable n
0.5
9
0.01
891
We can see that the smaller the greater n should we choose. It makes sense because the more rare the characteristic we want to analyze, the greater sample we should have to include people with this characteristic in it.
