A manufacturer of light bulbs has sampled 25 bulbs in order to determine the population mean life of the bulbs. The sample mean was 1200hrs with a standard deviation of 100. The manufacturer would like to know with 95% confidence, the internal values for population mean?
For 95%, Z = ± 1.96
Z = (score-mean)/SEm
SEm = SD/√n
Insert values and calculate.