2008 AMC 10B Problem 17

Attempt Problem 17 of the 2008 AMC 10B below, then check your answer against the professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2008 AMC 10B solutions, or check the answer key.

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17.

A poll shows that 70%70\% of all voters approve of the mayor's work. On three separate occasions a pollster selects a voter at random. What is the probability that on exactly one of these three occasions the voter approves of the mayor's work?

0.0630.063

0.1890.189

0.2330.233

0.3330.333

0.4410.441

Answer: B
Concepts:binomial probabilityindependent events
Difficulty rating: 1240
Solution:

Exactly one approval among three occasions arises in (31)=3\binom{3}{1}=3 ways, each with probability (0.7)(0.3)(0.3)=0.063.(0.7)(0.3)(0.3)=0.063.

The total is 30.063=0.189.3\cdot 0.063=0.189.

Thus, the correct answer is B.

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