The manager of a large office building needs to buy a large shipment of light bulbs. After reviewing specifications and prices from a number of suppliers, the choice is narrowed to two brandswhose specificationswith respect to price and quality appear identical. He purchases 40 bulbs of each brand and subjects them to an accelerated life test, recording hours to burnout, as shown in Table 5.17.

(a) The manager intends to buy the bulbs with a longer mean life. Do the data provide sufficient evidence to make a choice?

(b) To save labor expense, the owners have decided that all bulbs will be replaced when 10% have burned out. Is the decision in part

(a) still valid?
Is an alternate test possibly more useful? (Suggest the test only; do not perform.)
Table 5.17 Data for Exercise 10 Brand A Brand B Life (Hours) Life (Hours)
915 992 1034 1080 1235 1238 1248 1273 1137 1211 1211 1218 1275 1282 1298 1303 1260 1276 1289 1306 1307 1335 1337 1339 1319 1336 1360 1387 1360 1383 1384 1384 1400 1405 1419 1437 1388 1390 1390 1390 1488 1543 1581 1603 1394 1394 1403 1410 1606 1614 1635 1669 1417 1419 1423 1426 1683 1746 1752 1776 1430 1442 1448 1469 1881 1928 1940 1960 1478 1485 1486 1501 2029 2053 2063 2737 1508 1514 1515 1517 LO.1