The article "Leachate from Land Disposed Residential Construction Waste" (W. Weber, Y. Jang, et al., Journal of Environmental Engineering, 2002: 237-245) presents a study of contamination at landfills containing construction and demolition waste. Specimens of leachate were taken from a test site. Out of 42 specimens, 26 contained detectable levels of lead, 41 contained detectable levels of arsenic, and 32 contained detectable levels of chromium.
a. Find a 90% confidence interval for the probability that a specimen will contain a detectable level of lead.
b. Find a 95% confidence interval for the probability that a specimen will contain a detectable level of arsenic.
c. Find a 99% confidence interval for the probability that a specimen will contain a detectable level of chromium.