I AM SO LOST! please help me... PICTURE OF THE QUESTION IN COMMENTS...

Question

melzie · Answer

attachment

melzie · Answer

@mathmate

mathmate · Answer

This is a question of weighted averages.
Question gives:
w1=98.90% of C-12
and w2=1.100% C13.
The average atomic mass would be given by
w1*AMU(C-12)+w2*(AMU(C-13)
Do not forget to change w1 and w2 into decimals before multiplying, i.e.
w1=0.9890, w2=0.01100
The number of significant figures equals that least number of significant figures of the data, namely that of w1.

melzie · Answer

so it would look like:$$(12.000000)(0.9890)+(13.003354(0.01100)$$

amtran_bus · Answer

Exactly

mathmate · Answer

@melzie Exactly!
You need a rather accurate calculator/software to do the calculations, and you have to decide on the number of significant figures for your result.  A step which is very important in chemistry and physics.

melzie · Answer

Thank you so much! I think i understand it now :)

mathmate · Answer

You're welcome! 
Thank you for the testimonial.  At first sight I thought it was a sarcasm, but then I realized that you meant to thank me for not having given a direct answer!  Whew!
Have a great day!  :)

melzie · Answer

oh sorry i didnt mean it sarcastically lol