# Relative atomic mass?

Anyone knows how to solve this question?

Thanks

### 1 Answer

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- AdamLv 73 months agoFavorite Answer
Let y% be the percent abundance of ³⁰Si.

Then, the percent abundance of ²⁹Si = (100 - 92.2 - y)% = (7.8 - y)%

Relative atomic mass of Si:

28.0 × 92.2% + 29.0 × (7.8 - y)% + 30.0 × y% = 28.09

2581.6 + 226.2 - 29.0y + 30.0y = 2809

y = 1.2

Hence, the percent abundance of ³⁰Si = 1.2%

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