3 proposed changes to wording

1. Changed "our one-sided test applies only to the case when the true speed is GREATER or equal to 10 miles per hour above the posted speed limit" to "our one-sided test applies only to the case when the true speed is GREATER or equal to 5 miles per hour above the posted speed limit", because earlier in the lesson I read that "you are interested in knowing if the true average speed at which cars travel on this road during rush hour is greater than or equal to 5 miles per hour ABOVE the speed limit".

2. Changed "sometimes this is available if a subject has be studied extensively" to "sometimes this is available if a subject has been studied extensively".

3. Changed "if you are required to compute sigma from the data, then using a t-test is more appropriate" to "if you are required to estimate sigma from the data, then using a t-test is more appropriate". I think "estimate" makes it clear that the population standard deviation is un-known, while "compute" may confuse some students by implying that the t-test entails knowing the population standard deviation.