Jo can use either of two different routes, A or B, for her journey to school. She believes that route A has shorter journey times. She measures how long her journey takes for 17 journeys by route A and 12 journeys by route B. She ranks the 29 journeys in increasing order of time taken, and she finds that the sum of the ranks of the journeys by route B is 219. (a) Test at the 10% significance level whether route A has shorter journey times than route B. [8] (b) State an assumption about the 29 journeys which is necessary for the conclusion of the test to be valid. [1]