Question

Find the critical values: a. Determine the critical value z????/2 that corresponds to a level of confidence of 87%. (2 pts). b. Find the critical t-value t????/2 that corresponds to 92% confidence and n = 15. (2 pts). c. Determine the critical value for a left-tailed test of a population mean at the α = 0.025 level of significance based on a sample size of n = 18. (2 pts) d. Find the critical value for a two-tailed test of a population proportion with α = 0.08. (2 pts)

Answer 1

Answer:

a) $z_{\alpha/2}=-1.51$ and $z_{\alpha/2}=1.51$

b) $t_{\alpha/2}=-1.89$ and $t_{\alpha/2}=1.89$

c) $t_{\alpha/2}=-2.11$

d) $z_{\alpha/2}=-1.75$ and $z_{\alpha/2}=1.75$

Step-by-step explanation:

Part a

On this case the confidence is 87% or 0.87 so the significance level is $\alpha=1-0.87=0.13$ and $\alpha/2 =0.065$. On this case we can assume that is a bilateral test or a confidence interval so we will have two critical values.

We need values a,b on the normal standard distribution such that:

$P(Z$ or $P(Z>b)=0.065$ and in order to find it we can use the following code in excel:

"NORM.INV(0.065,0,1)" or "NORM.INV(1-0.065,0,1)", and we see that the critical values $z_{\alpha/2}=-1.51$ and $z_{\alpha/2}=1.51$

Part b

On this case the confidence is 92% or 0.92 so the significance level is $\alpha=1-0.92=0.08$ and $\alpha/2 =0.04$. On this case we can assume that is a bilateral test or a confidence interval so we will have two critical values.

First we need to calculate the degrees of freedom given by:

$df=n-1=15-1=14$

We need values b,c on the t distribution with 14 degrees of freddom such that:

$P(t_{(14)}$ or $P(t_{(14)}>c)=0.04$ and in order to find it we can use the following code in excel:

"T.INV(0.04,14)" or "T.INV(1-0.04,14)", and we see that the critical values $t_{\alpha/2}=-1.89$ and $t_{\alpha/2}=1.89$

Part c

The significance level is $\alpha=0.025$ and is a left tailed test. On this case we know that is a left tailed test so then we have just one critical value.

First we need to calculate the degrees of freedom given by:

$df=n-1=18-1=17$

We need a value c on the t distribution with 17 degrees of freddom such that:

$P(t_{(17)}$, and in order to find it we can use the following code in excel:

"T.INV(0.025,17)", and we see that the critical values $t_{\alpha/2}=-2.11$

Part d

The significance level is $\alpha=0.08$ and $\alpha/2 =0.04$. On this case we know that w ehave a two tailed proportion test, so we will have two critical values.

We need values a,b on the normal standard distribution such that:

$P(Z$ or $P(Z>b)=0.04$ and in order to find it we can use the following code in excel:

"NORM.INV(0.04,0,1)" or "NORM.INV(1-0.04,0,1)", and we see that the critical values $z_{\alpha/2}=-1.75$ and $z_{\alpha/2}=1.75$