Many electronic devices use disposable batteries which eventually have to be replaced Assume that for one particular brand and type of battery the distribution of the hours of useful power can be approximated well by a Normal model The mean is 140 hours and the standard deviation is 4 hours The marketing department wants to write a guarantee for battery life What lifespan should they quote so that they can expect 98 of the batteries to meet the guarantee z 00 01 02 5080 0 0 5000 5040 0 1 5398 5438 5478 0 2 0 3 Table entry 0 4 0 5 0 6 0 7 0 8 04 5120 05 06 5160 5199 5239 5517 5557 5596 5636 5793 5832 5871 5910 5948 5987 6179 6217 6255 6293 6331 6368 6554 6591 6628 6664 6700 6736 6915 6950 7019 6985 7054 7088 7257 7291 7324 7357 7389 7422 7580 7611 7642 7673 7704 7734 7764 7794 7881 7910 7939 7967 7995 8023 8051 8078 7454 8212 8238 8264 8289 8315 8340 8186 8461 8438 8531 8665 8686 8749 8869 8888 9049 9066 9207 9222 0245 9257 0 9 8159 1 0 8413 1 1 8643 1 2 8849 1 3 1 4 15 Z 9032 9192 9222 03 8485 8708 8907 9082 9236 9370 8508 8729 8925 9099 9251 9382 07 5279 5675 5714 08 5319 6026 6064 6103 6443 6480 6808 6844 7157 7190 8944 9115 9265 9394 6406 6772 7123 8554 8770 8962 9131 8577 8790 8980 09 5359 5753 7517 7486 7823 8106 8133 8365 8389 8599 8621 8810 8830 8997 9015 9162 9306 9429 9147 9292 9279 9406 9418 6141 6517 6879 7224 7549 7852 9177 9319 9441