Just noticed a few sales on the books I wrote a few years ago. I had forgotten about them since sales were minimal. I was just pleased to put out my work on algebra. Now looking at completing a long standing project involving math for kids K through 5.  Check out the link below for the books.

http://www.lulu.com/spotlight/KKauffman1969

As the school year is under way in many areas, don't forget my self help algebra books on lulu.com. Working on a kids book that has been stagnant lately, but getting back to it. Thanks for checking!

http://www.lulu.com/spotlight/KKauffman1969

Remember that the t distribution is more wide than the standard normal distribution, but at n gets larger and larger, the t distribution become approximately normal in nature.

The t-test is used when population standard deviation is not known. When we know that population is normally distributed, then we can use Z and also when population standard deviation is known, we can use Z