Confidence Intervals for Population Mean: Videos & Practice Problems

A nutrition lab is evaluating the sodium content in a new brand of vegetable soup and wants to estimate the average sodium level per serving. The lab requires the estimate to be accurate within $1.2$ milligrams of the true population mean with $90\%$ confidence. If the population standard deviation is known to be $1.9$ milligrams, what is the minimum number of soup servings they must test to meet this requirement?