To find out how much Mrs. Perez needs to write the check for, we subtract the amount she paid in cash from the total price of the washing machine.
Total price of the washing machine: $986.23
Amount paid in cash: $497.80
Now, we calculate the balance:
\[ \text{Balance} = \text{Total Price} - \text{Cash Paid} \] \[ \text{Balance} = 986.23 - 497.80 = 488.43 \]
Therefore, Mrs. Perez should write the check for $488.43.