I show how to find the appropriate z value (using the standard normal table) when calculating a confidence interval. The version of the table used in this video gives the area to the left of the z value (and not the area between 0 and z).

For those that use R, below is the R code to find the values (see the video for illustrations).

z value for a 95% interval:
qnorm(.975)
[1] 1.959964

z value for a 75% interval:
qnorm(.875)
[1] 1.150349