Question

A country is considering raising the speed limit on a road because they claim that the mean speed of vehicles is greater than 30 miles per hour. A random sample of 15 vehicles has a mean speed of 35 miles per hour and a standard deviation of 4.7 miles per hour. At ? = .01, do you have enough evidence to supprot the country's claim?
Calculate the p-value:

Answer 1

Answer:

We conclude that speed is greater than 30 miles per hour.

Step-by-step explanation:

We are given the following in the question:  

Population mean, μ =  30 miles per hour

Sample mean, $\bar{x}$ = 35 miles per hour

Sample size, n = 15

Alpha, α = 0.01

Sample standard deviation, s = 4.7 miles per hour

First, we design the null and the alternate hypothesis

$H_{0}: \mu = 30\text{ miles per hour}\\H_A: \mu > 30\text{ miles per hour}$

We use one-tailed(right) t test to perform this hypothesis.

Formula:

$t_{stat} = \displaystyle\frac{\bar{x} - \mu}{\frac{s}{\sqrt{n}} }$

Putting all the values, we have

$t_{stat} = \displaystyle\frac{35 - 30}{\frac{4.7}{\sqrt{15}} } = 4.120$

Now, $t_{critical} \text{ at 0.01 level of significance, 14 degree of freedom } = 2.624$

Since,                  

$t_{stat} > t_{critical}$

We fail to accept the null hypothesis and reject it. We accept the alternate hypothesis and conclude that speed is greater than 30 miles per hour.

We calculate the p-value.

P-value = 0.00052

Since p value is lower than the significance level, we reject the null hypothesis and accept the alternate hypothesis. We conclude that speed is greater than 30 miles per hour.