Free statistics software

More than a few.

The SPSS people have spent at least 30 years developing their software, so don't expect to find anything free that's close.

But if you have specific kinds of statistics in mind, there are lots of choices. Many have been developed by academics who put the packages together with grant money. That often means that they are not allowed to sell it commercially.  And, yes, there are some open source alternatives.

 Use this site as a starting point...

http://freestatistics.altervista.org/en/stat.php

However, I can't emphasize enough that whether you acquire free or commercial software, the user needs some solid statistical training.

Confidence interval for the population mean: Use of the t distribution

A toy manufacturer wants to see how long, on average, a new toy captures children's attention. He tests children selected at random and finds that their mean attention span is minutes with a standard deviation of minutes. If we assume that attention spans are normally distributed, find a confidence interval for the mean attention span of children playing with this new toy. Then complete the table below.

Carry your intermediate computations to at least three decimal places. Round your answers to one decimal place.

Confidence interval for the population mean: Use of the t distribution

A toy manufacturer wants to see how long, on average, a new toy captures children's attention. He tests children selected at random and finds that their mean attention span is minutes with a standard deviation of minutes. If we assume that attention spans are normally distributed, find a confidence interval for the mean attention span of children playing with this new toy. Then complete the table below.

Carry your intermediate computations to at least three decimal places. Round your answers to one decimal place.

A toy manufacturerer wants to see how long on average a new toy captures childrens attention.  He tests 20 children selected at random and finds that their mean attention span is 28 minutes with a standard deviation of 7 minutes.  If we assume that attention spans are normally distributed find a 95% confidence interval for the mean attention span of children playing with this new toy.  What is the lower limit of the confidence interval?  What is the upper limit of the confidence interval?