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nlcsa22

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1. For the number 100, I understand that there can be one, two, or three

significant figures. If there are three, then I understand that the assumed

uncertainty in the measurement (if no uncertainty is explicity stated) is 1 (perhaps even 2 or 3, but usually 1). So

we can then say 100 +/- 1. So the actual measurement could be as low as 99

or as high as 101. What would the uncertainty be if we were to say that only

two of the figures in 100 were significant (ie. the 1 and the middle 0)?

Would it be plus or minus 10 (meaning that the actual measurement would be

between 90 and 110)? And what would the uncertainty be if we were to say

that there was only one significant figure in 100 (ie. the 1)? Would it be plus or minus 100 (meaning that the actual measurement would be between 0

and 200)?

2. My textbook says that "it is good practice to keep an extra significant

figure or two throughout a calculation, and round off only in the final

result." Can you please explain this? An example would be helpful, too.

3. My textbook says that 1 in. = 2.54 cm. It says that this is exact, so the

2.54 has an infinite number of significant figures, not just 3. In an

example in the book, the author uses this conversion factor to convert 1

square inch to square centimeters. He writes 1sq.in. = (2.54cm)^2 =

6.45sq.cm. Now, 2.54*2.54 = 6.4516. Since 2.54 here has an infinite number

of significant figures, the 6.4516 also must have an infinite number of

significant figures. But the author rounded 6.4516 to 6.45. In doing so, was

he "clipping" the significant figures from infinity to 3, or do we still

consider the 6.45 to have an infinite number of significant figures? If the

former is true (ie. he reduced the significant figures from infinity to 3),

why did he do that?

4. One problem in my textbook involves a posted speed limit of 55 mph. Does

this have an infinite number of significant figures, since it's an exact

number?

Thanks very much