Calculating Averages?
posted by Alison
A certain element has four isotopes.
5.85% of has a mass of 53.93961 .
91.8% of has a mass of 55.934939 .
2.12% of has a mass of 56.93539 .
0.282% of has a mass of 57.93328 .
What is the average atomic mass of element ?
Express your answer numerically to three significant figures.

Alison
i got 56.2amu but it was wrong. i don't know how to find the average amu?

TutorCat
http://www.algebralab.org/practice/practice.aspx?file=algebra_averageatomicmass.xml

Reiny
I would suggest finding the 100% mass of each of the isotopes, adding those, then dividing by 4
I will find the 100% mass for the first one:
if 5.85% has a mass of 53.93961, then
100% has a mass of 53.93961/5.85*100 or 922.0446154
I could be way off base here, perhaps a chemist could enlighten us.
The webpage suggested by "TutorCat" makes sense to me. 
Kevin
just throwing out a number because i'm bored: 55.8741 was what i got. I'm no chemist, but i wanted to take a shot at it and now i'm curious how close the real answer is to mine.

A
55.8
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