The following data give the amount of money (in dollars) spent on textbooks by 18 students for the last academic year at a large university.
510 425 190 298 157 260 320 615 455
490 188 115 230 610 220 155 315 110
Test the hypothesis that the median amount spent on books at this university is $325 against the alternative that it is different using the large-sample sign test. Use α = 0.05.