A design engineer meаsured the service life оf а hаlоgen headlamp his cоmpany produces. On three recent production batches, he tested service life on random samples of four headlamps each. sample Service life (hours) 1 515 520 505 490 2 600 555 480 525 3 590 595 450 615 What is the LCL for the mean control chart, using 3-sigma control limits?