Answer:
[tex]\boxed{\text{40 u}}[/tex]
Explanation:
The atomic mass is the weighted average of the atomic masses of each isotope.
In a weighted average, we multiply each value by a number representing its relative importance.
In this problem, the percent abundance represents the relative importance of each isotope.
Data:
K-39 = 23 %
K-40 = 48 %
Calculations:
(a) Calculate % K-41
K-41 = 100 - 23 - 48 = 29 %
(b) Calculate atomic mass of sample
[tex]\begin{array}{cccc}\\\textbf{Isotope} & \textbf{Mass/u} & \textbf{Abundance} & \textbf{Contribution/u}\\\text{K-39} & 39.0 & 0.23 & 9.0\\\text{K-40} & 40.0 & 0.48 & 19.2\\\text{K-41} & 41.0 & 0.29 & 11.9\\ & \text{TOTAL} & = & 40.0\\\end{array}\\\text{The average atomic mass of the sample is }\boxed{\textbf{40 u}}[/tex]
