Question

A random sample of 100 people was taken. Eighty of the people in the sample favored Candidate A. We are interested in determining whether or not the proportion of the population in favor of Candidate A is significantly more than 75%. At a .05 level of significance, it can be concluded that the proportion of the population in favor of candidate A is _____.
a. significantly greater than 75%b.not significantly greater than 75%c. significantly greater than 80%d.not significantly greater than 80%

Answer 1

Answer:

Option b - not significantly greater than 75%.

Step-by-step explanation:

A random sample of 100 people was taken i.e. n=100

Eighty of the people in the sample favored Candidate i.e. x=80

We have used single sample proportion test,

$p=\frac{x}{n}$

$p=\frac{80}{100}$

$p=0.8$

Now we define hypothesis,

Null hypothesis $H_0$ : candidate A is significantly greater than 75%.

Alternative hypothesis $H_1$ : candidate A is not significantly greater than 75%.

Level of significance $\alpha=0.05$

Applying test statistic Z -proportion,

$Z=\frac{\widehat{p}-p_0}{\sqrt{\frac{p_0(1-p_0)}{n}}}$

Where, $\widehat{p}=80\%=0.80$ and $p=75%=0.75$

Substitute the values,

$Z=\frac{0.80-0.75}{\sqrt{\frac{0.75(1-0.75)}{100}}}$

$Z=\frac{0.80-0.75}{\sqrt{\frac{0.1875}{100}}}$

$Z=\frac{0.05}{0.0433}$

$Z=1.1547$

The p-value is

$P(Z>1.1547)=1-P(Z$

$P(Z>1.1547)=1-0.8789$

$P(Z>1.1547)=0.1241$

Now, the p-value is greater than the 0.05.

So we fail to reject the null hypothesis and conclude that the A is not significantly greater than 75%.

Therefore, Option b is correct.