A local firm in Quiapo Manila manufactures LED products that have a lifespan that is approximately normally distributed with a std. dev. of 40 hours. If a sample of 30 LED products has an average...

A local firm in Quiapo Manila manufactures LED products that have a lifespan that is approximately normally distributed with a std. dev. of 40 hours. If a sample of 30 LED products has an average lifespan of 790 hours,find a 98% confidence interval for the population mean of all LED products produced by this firm.