Question

Studies indicate that drinking water supplied by some old lead-lined city piping systems may contain harmful levels of lead. Based on data collected in a particular city it appears that the lead content in individual water specimens is normally distributed with mean 12 parts per billion and standard deviation 4 parts per billion. Specimens are classified as either S ("Safe"), M ("monitor") or DNC ('Do not Consume') [3] a. If a "safe" lead content in a water specimen is considered to be less than 15 parts per billion, what is the probability that a randomly selected water specimen is "safe"? [3] b. If 25 water specimens are collected at random what is the probability that their average lead content is less than 13 parts per billion? [4] c. A water specimen with lead content greater than 20 parts per billion is classified DNC. For 10 randomly selected water specimens give an expression for the prob- ability that exactly 6 are S and exactly one is DNC. Numerically evaluate this expression.

          Studies indicate that drinking water supplied by some old lead-lined city piping systems
may contain harmful levels of lead. Based on data collected in a particular city it
appears that the lead content in individual water specimens is normally distributed
with mean 12 parts per billion and standard deviation 4 parts per billion. Specimens
are classified as either S ("Safe"), M ("monitor") or DNC ('Do not Consume')
[3] a. If a "safe" lead content in a water specimen is considered to be less than 15 parts
per billion, what is the probability that a randomly selected water specimen is
"safe"?
[3] b. If 25 water specimens are collected at random what is the probability that their
average lead content is less than 13 parts per billion?
[4] c. A water specimen with lead content greater than 20 parts per billion is classified
DNC. For 10 randomly selected water specimens give an expression for the prob-
ability that exactly 6 are S and exactly one is DNC. Numerically evaluate this
expression.

Studies indicate that drinking water supplied by some old lead-lined city piping systems
may contain harmful levels of lead. Based on data collected in a particular city it
appears that the lead content in individual water specimens is normally distributed
with mean 12 parts per billion and standard deviation 4 parts per billion. Specimens
are classified as either S ("Safe"), M ("monitor") or DNC ('Do not Consume')
[3] a. If a "safe" lead content in a water specimen is considered to be less than 15 parts
per billion, what is the probability that a randomly selected water specimen is
"safe"?
[3] b. If 25 water specimens are collected at random what is the probability that their
average lead content is less than 13 parts per billion?
[4] c. A water specimen with lead content greater than 20 parts per billion is classified
DNC. For 10 randomly selected water specimens give an expression for the prob-
ability that exactly 6 are S and exactly one is DNC. Numerically evaluate this
expression.

Added by Vicenta D.

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