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?

Answer 1

For 95%, Z = ± 1.96

Z = (score-mean)/SEm

SEm = SD/√n

Insert values and calculate.