Lead and arsenic can contaminate drinking water systems in a city.The probabilit
ID: 3354113 • Letter: L
Question
Lead and arsenic can contaminate drinking water systems in a city.The probability of lead and arsenic contamination is 0.2 and 0.1, respectively. Assume that contaminations by lead and by arsenic are statistically independent.
a.
What is the probability that the drinking water system in any given city is contaminated?
b.
Six cities are currently at the risks of drinking water contamination. Four of the cities are exposed to lead contamination; and the other 2 are exposed to arsenic contamination. A group of undergrad students wanted to investigate the water contamination situation at 2 of the 6 cities. What is the probability that the two cities that they chose are both at risk of lead contamination?
Explanation / Answer
a) probability that the drinking water system in any given city is contaminated
=P(lead contamination)+P(arsenic contamination)-P(lead and arsenic contamination)
=0.2+0.1-0.2*0.1=0.28
b) probability that the two cities that they chose are both at risk of lead contamination
=P(first from lead comtamination)*P(second is exponsed to lead comtamination) =(4/6)*(3/6)=2/6= 1/3
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