The average atomic mass of a sample of an element X is 16.2 u, what are the percentages of isotopes `"_8^16X` and `"_8^18X` in the sample?

Explanation

Let percentage of `._(8)^(16)X = x`
`therefore` % age of `._(8)^(18)X = (100 - x)`.
`therefore` Average atomic mass of the given element
`= 16 xx (x)/(100) + 18 xx ((100 - x))/(100)`
`therefore" "16.2 = (16 xx x)/(100) + (18 xx (100 - x))/(100)`
`1620 = 16x + 1800 - 18x`
`2x = 1800 - 1620 = 180`
`therefore` x = 90
`therefore` % age of `._(8)^(16)X` in the sample = 90%
% age of `._(8)^(18)X` in the sample = 100 - 90 = 10%