# Please can someone help with with this calculation for atomic mass

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1. Said what I wanted to say above ...
2. (Original post by JackT2000)
Said what I wanted to say above ...
3. Relative atomic mass = ((isotope number X abundance)+(isotope number X abundance)) / 100

The abundance is the percentage

So, in your case:

(63 X 69) + (65 X 31) / 100 = 63.62

It is best to try to round your numbers to 3 significant figures, unless the question specifies otherwise, so in this case the answer would be 63.6. However, 63.62 would probably still give you full marks in the exam.

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