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An urn contains balls numbered 1 through 20. A ball is chosen, returned to the urn, and a second ball is chosen. What is the probability that the first and second balls will be a 8?A. 1/40B. 1/10C. 1/20D. 1/400

Sagot :

An urn contains balls numbered from 1 through 20

The formula for probability is

[tex]\text{Probability}=\frac{\operatorname{Re}quired\text{ outcome}}{Total\text{ outcome}}[/tex]

Where the total outcome = 20

Since, the first ball was replaced after chosen, then the two events are independent of each other

Let the probability that a first ball is taken be represents by P(F)

Let the probability that a second ball is taken be represents by P(S)

The probability that a first ball is chosen with replacement is

[tex]\begin{gathered} P(F)=\frac{1}{20} \\ \text{For a ball picked, required outcome is 1} \end{gathered}[/tex]

Since there is a replacement, the probability that a second ball is chosen and will be 8 is

[tex]\begin{gathered} P(S)=\frac{1}{20} \\ \text{Note: only a ball is numbered as 8 so the required outcome is 1} \\ \end{gathered}[/tex]

Probability that a first ball is chosen and a second ball is chosen is

[tex]P=P(F)\times P(S)=\frac{1}{20}\times\frac{1}{20}=\frac{1}{400}[/tex]

Hence, answer is D