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What is the standard deviation of the values of the 20 coins in a certain jar ?
1. The average (arithmetic mean ) value of the coins in the jar is 25 cents .
2. All 20 coins in the jar have the same value .
Target question: What is the standard deviation of the values of the 20 coins in a certain jar ? Statement 1: The average (arithmetic mean ) value of the coins in the jar is 25 cents . There are several cases that satisfy statement 1. Here are two:
Case a: All 20 coins are quarters (each is worth $0.25). This meets this condition that the average value is 25 cents. In this case,
the standard deviation EQUALS 0Case b: The 20 coins are NOT all quarters. In this case,
the standard deviation does NOT equal 0Since we cannot answer the
target question with certainty, statement 1 is NOT SUFFICIENT
Statement 2: All 20 coins in the jar have the same value The means
the standard deviation EQUALS 0Since we can answer the
target question with certainty, statement 2 is SUFFICIENT
Answer: B
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