CHEMISTRY CHALLENGE PROBLEM (Help with solving)?

Question

A person weighed 15 pennies on a balance and recorded the following masses (grams):

3.112

2.467

3.129

3.053

3.081

3.109

3.079

2.545

3.054

3.131

3.059

2.518

3.050

3.072

3.064

Curious about the results, he looked at the dates on each penny. Two of the light pennies were minted in 1983 & one in 1982. The dates on the 12 heavier pennies ranged from 1970 to 1982. Two of the 12 heavier pennies were minted in 1982.

QUESTION: The person calculated the average mass of 12 heavy pennies. He expressed this average as 3.0828g +/- 0.0482g

What is wrong with the numbers in this result, and how should the value be expressed?

I need help on HOW to get the answer, not necessarily just the answer.

Answer 1

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