Convert the percentage abundances to fractional abundances.

The fractional abundance is the percentage abundance divided by 100.
For $^{35}\text{Cl}$: $75.4\% = \frac{75.4}{100} = 0.754$
For $^{37}\text{Cl}$: $24.6\% = \frac{24.6}{100} = 0.246$

The average atomic mass is calculated by summing the products of each isotope's mass and its fractional abundance.

We assume the isotopic masses are approximately equal to their mass numbers, i.e., 35 amu for $^{35}\text{Cl}$ and 37 amu for $^{37}\text{Cl}$.

The average atomic mass of chlorine is $\text{35.492 amu}$.