In establishing warranties on HDTV's sets, the manufacturer wants to set the limits so that few will need repair at manufacturer expense. On the other hand, the warranty period must be long enough to make the purchase attractive to the buyer. For a new HDTV the mean number of months until repairs are needed is 36.84 with a standard deviation of 3.34 months. Where should the warranty limits be set so that only 10% of the HDTV's need repairs at the manufacturer's expense?" I am unsure whether z = 1.28, making the answer 32.56, or z = -1.28, making the answer 41.12. Please explain which it is and why. Thank you