Section 8 3 26 Confidence Intervals for a Population Mean Standard Deviation Known Contaminated water In a sample of 42 water specimens taken from a construction site 26 contained detectable levels of lead a Construct a 90 confidence interval for the proportion of water specimens that contain detectable levels of lead b Construct a 95 confidence interval for the proportion of water specimens that contain detectable levels of lead c What is the effect of increasing the level of confidence on the width of the interval