To find out how much May will write the check for, subtract the amount she paid in cash from the total cost of the washing machine.
Total cost of washing machine: $986.23
Amount paid in cash: $497.80
Now, perform the subtraction:
\[ \text{Amount to write a check for} = \text{Total cost} - \text{Cash paid} \] \[ \text{Amount to write a check for} = 986.23 - 497.80 = 488.43 \]
May will write the check for $488.43.