probability and statistics

Return Subm 1 point Bacterial colonies were counted on 12 plates. There were two observers, and the plate counts obtained were as follows: Observer 1 Observer 2 Difference Plate Number 139 191 121 181 163 143 191 234 -19 179 250 218 239 297 289 165 201 -36 Test whether on average bacterial colony count of Observer 1 is less than that for Observer 2 (use Observer 1 - Observer 2) at 10% level of significance. What is the test statistic