Final answer:
In Cushing's syndrome, serum potassium levels will typically be low due to the overproduction of cortisol and decreased aldosterone.
Step-by-step explanation:
In Cushing's syndrome, the serum potassium levels will typically be low. This is due to the overproduction of cortisol, a hormone that causes potassium to be excreted in the urine. Additionally, aldosterone, another hormone involved in potassium regulation, is decreased in Cushing's syndrome, further contributing to low serum potassium levels.