Significant Figures

Significant figures are the numbers in a measurement that make it more precise.  More s.f = more precise!
All the s.f. are exact except for the last digit because they have been measured. The last digit is uncertain because it is just a best estimate. 

Rules for determining the amount of s.f. in a number:
1)     All digits from 1-9 are significant.
            -2435 = four s.f.
2)     0s preceding the number(leading zeros) do not count.
            -0.24 = two s.f.
3)     0s following the number(whole numbers) do not count unless there is a decimal point.  They are just there as placeholders.
            -480 = two s.f.
            -480. = three s.f.
4)     0s after digits in decimal numbers count because they represent an exact value of zero.
            -9.8740 = five s.f.
            -0.03274000 = seven s.f.
5)     0s between two digits always count.
            -93.40200008 = ten s.f.

Exact Numbers have an infinite amount of zeros.  These include things that can be directly counted or conversion factors. 

 

How many penguins are there?   Think hard!

You can't say there are 4.0045 or 4.2 penguins because you can't have 0.0045 of a penguin.  There are only 4.