Calculation of percentage of isotopes — task. Chemistry CBSE Live product, Class 9.

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The average atomic mass of a sample of an element X is $10.8$ u. What are the percentages of isotopes $X^{10}$ and $X^{11}$ in the sample?

$\begin{array}{l} (\frac{10 \times x}{100}) + \frac{11 (100 - x)}{100} = 10.8 \\ \frac{10 x - 11 x + 1100}{100} = 10.8 \\ - x + 1100 = 10.8 \times 100 \end{array}$

$x = 70$ and $(100 - x) = 30$
$x = 90$ and $(100 - x) = 10$
$x = 20$ and $(100 - x) = 80$
$x = 90$ and $(100 - x) = 10$

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5. Calculation of percentage of isotopes

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