How would you go about to solve this quesiton? I thought that to calculate this i had to set up an equation as:(adsbygoogle = window.adsbygoogle || []).push({});

let x = the percentage of 85-Rb

84.91*x + 86.91*(1-x) = 85

x = 96%, but that's obviously wrong.

How do i solve this question?

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# Atomic mass: Isotope question

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