Significant Figures

Significant Figures

Rules for Counting Significant Figures

• Any number 1-9 is significant

• 0 in LAST DECIMAL PLACE is significant

• 0 in BETWEEN significant digits is significant

Examples

• a.  both 0's are significant because one is in final decimal place and the other is between significant digits.

• b.  all 4 0's are significant because one is in final decimal place and the others are between significant digits.

• c. all 3 0's are significant because one is in the final decimal place and the others are between significant digits.

• d.  only 1 of the 0's is significant because it is between significant digits.   The others are not AFTER the decimal  

But Why? ROUNDING!!

• Whenever you calculate numbers in science the calculator will give you a bunch of numbers.

• NOT ALL THOSE NUMBERS ARE SIGNIFICANT!!!

• Why?  Because you answer can only be as precise as the LEAST precise measurement you used in your calculation.

• There are 2 ways to round using significant figures.

Rounding Rules for + and - with Sig Figs:

• Add or Subtract numbers as usual.

• The answer needs to be rounded to the LEAST amount of DECIMAL PLACES in the measurements you added or subtracted.

• Use rounding rules you learned in middle school to figure out if you need to round up or leave that decimal place.

Rounding Rules for x and / Sig Figs:

• Count number of sig figs in each number.

• Perform the calculation

• Round the answer to the LEAST amount of SIG FIGS as the measurements you calculated.  

BUT, BUT, BUT!!  What if I CANT round to the correct number of sig figs???

• There is always a way!!!

• Can use SCIENTIFIC NOTATION TO MAKE IT WORK FOR YOU!!!

• You only count the sig figs in the part before the x 10 part.

This is the end of Sig Figs!   

• please email me with any questions.

• Another great tutorial on this topic can be found at:

• https://www.youtube.com/watch?v=6oj4y0d44nQ