Please help answer this question. Thank you.

Twenty patients, 10 of normal weight and 10 severely over- weight underwent an exercise stress test, in which they had to lift a progressively increasing load for up to 12min, but they were allowed to stop earlier if they could do no more. On two occasions the equipment failed before 12min. The times (in min) achieved were: Normal weight: 4, 10, 12*, 2, 8, 12*, 3+, 6, 9, 12* Overweight: 7+, 5, 11, 6, 3, 9, 4, 1, 7, 12* *Reached end of test; lequipment failure. (I am grateful to C Osmond for these data)