# Thread: Complety lost on stastics problem!

1. ## Complety lost on stastics problem!

No matter how I approach it..i don't get it!

A recent study of 25 students reported that they spend an average of $18.53 per week on gas. The standard deviation of the sample was$3.00. Find the 95% confidence interval of the true mean.

2. Originally Posted by Mahoganybeauty06
No matter how I approach it..i don't get it!

A recent study of 25 students reported that they spend an average of $18.53 per week on gas. The standard deviation of the sample was$3.00. Find the 95% confidence interval of the true mean.
The formula you need can be found here: Confidence Intervals

The formula will also be in your class notes and textbook. Please show what you've tried and say where you get stuck.

3. Originally Posted by Mahoganybeauty06
No matter how I approach it..i don't get it!

A recent study of 25 students reported that they spend an average of $18.53 per week on gas. The standard deviation of the sample was$3.00. Find the 95% confidence interval of the true mean.
By the Central Limit Theorem

$Z=\displaystyle\huge\frac{\bar{X}-\mu}{\left(\frac{\sigma}{\sqrt{n}}\right)}$

where $\sigma$ is the population SD, $\mu$ is the population mean, $n$ is the sample size,

$\bar{X}$ is the sample mean and $\frac{\sigma}{\sqrt{n}}$ is the sample SD.

The 95% interval ranges from 2.5% to 97.5%.

Locate the Z-score for 97.5% and use the values given to rearrange the equation for $\mu$