Many freeways have service (or logo) signs that give information on attractions, camping, lodging, food, and gas services prior to off-ramps. These signs typically do not provide information on distances. The article Evaluation of Adding Distance Information to Freeway-Specific Service (Logo) Signs (J. of Transp. Engr., 2011; 78-888) reported that in one investigation, six sites along Virginia interstate high ways where service signs are posted were selected. For each site, crash data was obtained for a three-year period before distance information was added to the service signs and for a one-year period afterward. The number of crashes per year before and after the sign changes were as follows: Before: 15 26 66 115 62 64
After: 16 24 42 80 78 73
The cited article included the statement A paired t test was performed to determine whether there was any change in the mean number of crashes before and after the addition of distance information on the signs. Carry out such a test. [Note: The relevant normal probability plot shows a substantial linear pattern.] a seventh site were to be randomly selected among bearing service signs, between what values predict the difference in number of crashes to lie?